You really haven't addressed it. Maybe I'm not being clear enough in my question: I want to know a made up scenario where this Tantiv IV crew could make any kind of difference in the outcome. You're saying to kill them no matter what the risk and I'm saying the risk is so inconcievably small that it just doesn't matter.
The funny thing about this entire argument is you're as subjective with your POV as I am with mine, which makes it completely pointless.

But here's my point again... {Hypothetical} The Tantive IV, which has been hyper jumping trying to evade the Devastator for some time, has had time to at least attempt to analyze the plans. They've looked them over... Some crewmen involved have ideas of what the Death Star may or may not have as a weak point, or possible weak points, among them the exhaust port.
The Tantive IV is finally overrun in the Tatooine Systyem where some of the crew survive the assault from the Devastator, are interrogated, reveal nothing, and are sent to a penal world of some sort.
Since this is all hypothetical, let's say the Death Star destroys Alderaan, Leia's dead, etc.
Somehow, some of these survivors taken prisoner escape... however. It can happen, so that's the main point.
They take the information to whoever is left. How big/small the rebellion is, again, is subjective, but the EU says it's a lot larger than just Yavin IV... Again, choose to argue that, search Wookieepedia, whatever. It's only "small" by comparison. In SW terms, small can still be fairly sizable, but I digress.
Anyway, they get this info back to whatever remains of the Rebellion other than the Yavin base, and there's now new hope... They put together the same attack as in the film, and the same result can happen.
To me it's just a simple wiping clean of any possible scenario... Slim as it may be, a chance is a chance, and I think if the Emperor or Vader thought anyone had any inside track, they'd want that person gone.
You're acknowledging my point, you're just saying it's so negligible to you that you think the Empire wouldn't bother. I'm saying I think the Emperor or Vader would be more thorough than that if they were aware of who those people were. They'd likely never know what they knew, or didn't know, they'd just want them dead to be certain. That's all.
You also argue that these guys are grunts that probably don't have any useful information. So your assumption is that they know enough about the Death Star to potentially cause it's downfall if they could get away, but they couldn't possibly have any useful knowledge about the inner workings of the Rebellion?
This whole thing is a subjective assumption. Yours are too.

But you're not totally getting what I'm saying here Justin. Their usefulness as slaves and things, I look at as a completely unimportant argument since, to me, the Death Star's security/importance would outweigh whether they were a ship of Albert Einstein's or a ship of conscripts from a penal colony. I understand your point on potential importance, I just think the Empire would put that on the backburner to the Death Star. It's kind of the "big thing" of that timeframe.
I don't assume they know anything about the Death Star though... I'd say the ship is largely made up of the men to crew it and make it function, not scientists, but it's hard to say who is on board there that maybe could have analyzed and figured out anything about the Death Star. Any individual could hold any ammount of knowledge about the Death Star, the inner workings of the REbellion, or whatever. What I am assuming though, is the Empire doesn't know exactly what any survivor may or may not know, and what their skillset might be, or how well they may just be resisting the interrogations... I'm assuming nothing here other than the Empire isn't aware of EVERY fact, and so to be thorough, they may want to kill everyone because the Death Star is the primary focal point of the argument of whether to kill the crew or not.
They want the plans back, desperately. That's a fact. Vader's pissed they're gone. So why would you take any risk that any person you captured could have any shred of any detail of those plans in his head.
I think a lot of the argument could be based on the time passed... When were they beamed to the Tantive IV? How long did it take the Devastator to catch it? Etc. Could it have been hours? Days? A couple weeks of pursuit? I lean towards it being a decent ammount of time. Longer than hours, maybe even days of pursuit with some narrow escapes and whatnot. All subjective though, again.
Those are some really subjective assumptions. Honestly, I can see the Empire not really caring one way or another about these guys. If they killed the crew, I think it's more out of simple convenience than any perceived risk of a leak.
Maybe convenience is a good way to word this... It's convenient, to kill the crew rather than deal with them. Deal with their disparagy of the Empire, deal with transporting them, deal with any information they may or may not have... It's just convenient.
I'm not discussing it as if Vader's biting his fingernails worried these guys have the key to bring down the Empire with one stroke. I think "convenience" is a good way to describe offing them. Like I said a while back... no fuss, no muss.
Sure it's a big galaxy, but how big is the rebellion? They launch a few dozen ships to attack the death star out of their main base. That's it? You want to talk risk - how about the risk that these guys know something valuable that you're not going to get out of them if they're dead?
Again... Depends on what you believe. If you only take the movies at face value, the Rebellion is contained to the temples on Massassi with not a lot more available.
If you believe all the other crap LFL has put out, the Rebellion is ONLY small in relative terms. It's a big galaxy... A small rebellion in it is a hell of a lot larger than anything Earth could put together. It's made up of many planets by our standards, few by the SW galaxy's standards. The Rebellion has many ships if you gathered them all, but few if you compared it to the Empire. They have many men compared to all the armies on our planet, few compared to the countless numbers the Empire has at its fingertips.
The Yavin IV base is their main base... It's secret, has a sizable force, they can conduct devastating raids against the Empire from it that have caused the Empire to raise an eyebrow... They have other bases though. And ships.
Again though, depends on what you accept and what you don't... If EU's your thing, the Empire would have devastated the Alliance at Yavin IV but would've had a lot of work ahead of it to eradicate the Rebels entirely.
About the risk of killing the Rebel prisoners... I wholely believe they keep them through some interrogation, but at some point feel they exhaust them. They either give up their info or don't. Like Leia... She was tortured, didn't give up what they wanted to hear, so she was scheduled for execution.
Surely the Empire has a better system for managing security codes than a handful of scattered, poorly funded rebels.
Again, a lot of that weighs on what you consider "real" as far as Star Wars goes.
The films imply though, that the Alliance is a seemingly organized military... They're spending money on rank badges, and matching winter uniforms, but they don't have a plan in place if there's a possible security breach despite their very existance relying upon those plans?
And just to build on that idea, keep in mind that the Empire was not done just because the Emperor and Second Death Star were blown away. In much the same way, other Rebels or new Rebels would still be out there even if the Yavin base was destroyed. If you were confident that you're about to blow away the rebel base like Tarkin was, then the smart priority would be on keeping these prisoners to extract any knowledge you could from them.
I'd agree except that this relies, heavily, on assuming that Rebel prisoners are tough to come by too... Not that you want to pass on information where you can get it, but do they really NEED more, to the point they would put the Death Star in any kind of risk no matter how incredibly miniscule that risk may be?
Also, if information is so important, why would you schedule Leia's execution then? Yeah, Tarkin's mad, but you're making the argument that every Rebel is of value to the point they'd take them no matter how small their perceived value, so wouldn't Leia be an ultimate prize? That's like the allies capturing Rommel, but because Patton was in a pissy humor he kills him.
Disagree. The Death Star did fail and we don't see any evidence that all the worlds joined up to overthrow him.
I'll double disagree then!

Tagge himself says to Motti, Tarkin, Vader, etc., that the, "Rebellion is stronger than you realize". He argues that the Emperor will not be able to maintain control against the Imperial Senate without the beaucracy. Tarkin cites the Death Star as the means of control.
The Death Star is dead shortly thereafter in the film... By all EU accounts, it's a pretty devastating blow for the Empire. It doesn't spell their end, but (and again, EU's all in what you accept or don't accept) it does give the Rebellion help that was fearful before. And isn't that only logical? That as word spread that the Empire had built something they used to destroy a "peaceful" world, you honestly don't think other planets now might become openly rebellious? Not to mention, they've now had their say in the politics of the galaxy taken away by the Emperor because he figured he'd have the ruler to crack them on the knuckles with... I don't buy that in the slightest. The films and EU both at least lend credence to the thought that the Empire would have a new set of troubles post-ANH.
I'm not sure when the Calmari joined up - maybe the loss of the Death Star contributed to them joining the rebellion, but that's just my speculation. The Empire had a pretty firm grasp on the galaxy even without the Death Star - the DS is just meant to be an ultimate solution.
Again, that's a presumption on your part... Before the Death Star, the Rebellion had already won its first major victory against them. Tagge was clearly distressed by them.
The Emperor and Tarkin were supremely confident in the station, so much so that they disband the senate before the DS even goes live. I can't see those guys really caring one way or another about the survivng crerw making any kind of impact whatsoever.
Why care if you kill them then? You've got the ability to do what you want... The Rebellion can make trouble but you can wipe them out wherever they go, and whoever gives them safe haven.
Now, if the Empire was run by Hasbro, I could definitely see them killing people off to make sure no one gets the news out before them. 
Trust me, they don't care. It's more likely the sites would be at each other's throats. Hasbro just would sit back and laugh at the free advertising.
