I hate him... Bastard.
The focus on the word "constant" I do think is a stretch and I agree with Rob that it means any number of things... So to that extent, I think mutually agreed-to swinging is what it is, and not (to me) morally or ethically wrong...
That's what it boils down to really though. Infidelity is a question of ethics and morals. Do you feel it's wrong to do this, and if so it's wrong if you do this... Nothing more, nothing less. If you feel it's your right to "cheat", it simply isn't within your moral/ethical code then... What the topic is about though is infidelity which I tend to assume means that the people discussing it agree it's "wrong" so that to do that act is to basically be immoral to their own beliefs. Others may disagree... I was just working under the assumption for (at least) the majority.
I don't look at swinging as immoral, someone may, but it's not my business... And if everyone in it is in agreeance and everything's on the up-and-up (my turn for a

I guess) then hey, whatever... I definitely don't view cheating/infidelity and "swinging" as being the same though. Again though, that's really a moral decision despite the definitions even. Some moral codes are going to label "swinging" as infidelity despite the definition I'd think.
I don't know... Anyway to me it's not cheating but I don't think you're doing yourself any favors if you actually care about who you're with, but what do I know...