The safety issue is not insignificant, I will agree with that. Especially when you're deal with a rocket at speed with volatile fuel on board.
But it does seem that there can be an increase in risk variables with a sea landing, notably with the weather. Most carrier rated pilots say that landing at sea is a big challenge not just because of the small field of an aircraft carrier and the incredibly small target of the arresting wires. But also because the deck is subject to pitching and rolling based on the sea state (frequency and height of waves).
The rocket touchdown is probably much more like a helicopter landing since it's a vertical approach to a relatively static landing zone. But given the automated nature of the control systems for the drone ship as well as the rocket, is the guidance software really up to this sort of challenge on a regular basis?