Lot of replies, I haven't read all. Opinions do vary.
I have several friends I trust enough to loan them my guns.
But, my main shooting passion is traditional muzzle loaders. I have three very fine custom made rifles. Even though I trust my friends, 'stuff' happens. If they were to damage one I know it would affect the friendship for a long time. Therefore, not worth the risk. My modern guns, I would happily loan. I have nothing fancy in modern. It would be like loaning a shovel.