Now this is an interesting one, and I've been trying to decide where I stand on this. To me it sort of sounds like 2 questions rather than 1.
Firstly, how do I feel about random people (or guitarists) just picking up my bass? In short, I don't allow it. In my experience, good musicians will ALWAYS ask first (and I'll almost certainly say yes), and I wouldn't even consider picking up sone elses instrument of whatever type or perceived quality without asking first. It's how I was brung up, and it seems like a good rule of thumb to me.
But the guys I choose to be in a band with are not just random people (or guitarists). I guess I'm lucky in that they are like brothers to me, and I would not question any of them reaching for my bass any time. They can't play it (and I'm happy to remind them), but they are welcome to try. They would never do anything to damage any of my gear - for some, years on the road with them means I just know that. For the rest, if I have any doubt I'd be working with someone else. We tease each other, joke with each other, play tricks on each other, even fight woth each other, but in the end respect each other.
It's sad that so many folks here seem to be trapped in gigs with people that they don't seem to trust, respect or even like. I can't imagine how a band like that could work musically, but you obviously make it work, and get my respect (and sympathy) for that. I guess it's the curse of playing for a living rather than because you like it.