My insurance covers me if a jackoff rear ends my bike. Plus, it means I get a new bike. As far as the versatility of a roof rack goes, I don't do any of that other stuff to necessitate the versatility...no kayaking, no skiing, no snowboarding.
It takes 10 seconds to remove my bike from my hitch mount rack, and another 10 to remove the rack itself when I'm not using it (no unnecessary extra weight). The roof mount on the other hand, well that's another story. You have the possibility of slipping while atop the car and scratching both the car and possibly ruining your bike (insurance would not cover that).
I have an ARB roof rack that I use for gear when camping, but truthfully I don't keep it on that much. My car wash I go to doesn't allow roof racks because of all the mechanisms that do the washing.
Bottom line: If you're super Xtreme and do all sorts of outdoor activities 24/7 then maybe a roof rack will be your choice. But if you're just needing to carry your bikes, go hitch mount.