I have the Thule rear hitch rack, and believe it or not, with the factory lock, you can strip 2 bikes off in 20 seconds. The factory lock (over the front wheel) leaves a lot to be desired. As far as getting hit, the other driver's insurance SHOULD cover it. You hitting overhang...outta yer pocket. That's one reason why I got the hitch rack. Besides, I have a Jeep Grand Cherokee, and I can't lift the bike onto the roof that high.....I'd fall on my ass with my bike on top of me why my friend laughs his ass off.....
I bought kryptonite cables and a U-lock for a deterrent. Nothing is theft proof. Where there is a will, there is a way.
Sorry to hear about your misfortune.....