Some musicians play well with others. Some don't. I don't think it has anything to do with whether or not they are amplified. I've played a lot with acoustic and electric instruments on the same stage it's never been a problem.
Exactly. If someone deliberately plays without concern for the sound of the group, they are just being a jerk. It is just not acceptable and I think it is OK to ask them to leave - just like you would with a loud drunk. In reality, there are few people who act out like that and, like you say John P, it's not usually a problem and it has nothing to do with being amplified.