It's just a bike...If I think they can ride and aren't likely to dump my bike (and are able to pay for the damage if they do), I have no issue with it...
I'm the only one who rides mine. I read someplace that high percentage of accidents occur when someone is riding a bike that isn't theirs. Don't know if it's true but it makes sense.
I let people I trust and currently have a bike. With the understanding I get to use their bike while mine is in the shop, if anything should happen.
My Pops was at the Little Bear in Evergreen CO and started talking to guy about his bike parked out front because he has the same one back home. The dude threw my Pops the keys and let him take it for a hour ride through the hills.
That was very cool of him, but I think it's crazy.
I have two guys that I ride with alot, either are welcome to ride it whenever. I wouldn't let just anybody, I want to know their riding ability first. Anyway, if it did get wrecked they haven't quit making them yet.