I have two very close friends, both avid gun collectors and shooters, who I know take very good care of their own guns. I'd loan a gun to either of them should they request it (doubt that they would). Other than that, if someone wants to fire one of my guns when I'm at the range, fine. But no lending.
Likewise I would not ask to borrow a gun from anyone. Asking to shoot one when someone is at the range is fine.