I don't know how I feel about the collaboration argument. It sounds ok, but how much do I really collaborate with the English and social studies teacher at the high school level? The answer is never. I collaborate often with other math teachers, and occasionally a science teacher, but that's it. Also, if you think about other work places where people make different amounts of money (i.e. an office of some sort), does that really prohibit collaboration? I'm not sure it does. Again, I'm not 100% in favor of this, just thinking it through.