I've been in both situations before. People have asked to play through my gear. In my situations, the bands are generally respectful of my gear, and I always talk to the bass player for a minute just to lay out my requests for him not to max out the gain, etc. Sometimes, the other band did bring their gear, and they are asked by the sound guy or whatever to see if they can share gear to minimize setup time.
On the other hand, I played bass for this guy that was a literal compulsive liar. He made stuff up in his own head, and believed his lies. Anyways, we played a festival in Louisville, KY, and I had my gear to take with me on the bus. But the guy told me that I didn't need to bring it, because he already talked to the other bands and I could just use their gear. I was uncomfortable with that, but I agreed.
So, we get to the show, and low and behold, no one knew anything about me using their gear. But luckily for me, the bass player in the band we played after, Red Jumpsuit Apparatus, was very nice and let me use his Ampeg stack.
So I see it both ways. Sometimes, not everyone is a loser that shows up without any gear and just wants to ROCK! Most of the time, people are very courteous and thankful to use my gear if I let them.