This topic surfaces pretty regularly and I'm always interested to see the wildly varying opinions and experiences. Part of it is age-dependent as my gear and the way I gig now in my mid 50's is certainly different than when I was 19. Part of it is psychology dependent, especially wrt OCD (or more correctly, CDO - the letters should be in alphabetical order).
As for the question, my answer is just as my attorney ex-wife always advised - "it depends." I have been (and still am) house bassist for various jams. In that case, my amp is de facto everyone's amp assuming there are bass players that came for the jam. I can say all I want, but some guys will do what they will do. If they really are out of control I can just walk up and unplug them, and deal with the invariable mini drama that unfolds. Part of the gig. Over the probably 25 years I've been doing those, I can count on one hand the number of guys who really got out of hand.
If my band is on the bill with other bands, I'm not going to expect to loan my gear. A lot of places that do showcase gigs insist you use their backline so it is a non-issue. For other places, sometimes you stack gear with early load-in, other times you're doing the "stop talking to the girl and get your crap off the stage, I need to bring mine up" dance. In the former, it will be evident if someone is expecting to borrow gear. For the latter - I'm usually not sticking around so I'm not going to leave my gear up. Depends on the scene and what else is going on. Thankfully these days we're either the only band playing, or we're doing a set then I'm doing a quick tear down and leaving (anti-social evidently).
If another player is in a spot, I might loan depending on the situation and the vibe. Stuff happens, and I've been helped by the kindness of other musicians in the past. But if I'm not feeling it, I'm not doing it. These days I usually don't have to borrow anything as I've typically got backups for everything but I'm able to do that - not everyone can.
As for my bass, I have let some people check them out (though not borrow for a gig) - even the Fodera. Totally depends on the situation. I will say that the unlined fretless 5s get very few requests
