I have no problem with teachers ... most bend over backwards to go above and beyond for their students. Anecdotally, I have seen this in my sister ... a 30+ year teaching veteran and strong union member ... from spending money out of her pocket to provide supplies, clothing and food for her students.
Nor do I have a problem with teachers' unions ... I also know that school systems that have strong unions also tend towards the top of school systems.
I, also, agree that teachers spend a great deal of time talking about how to make things better for the students ... and I would venture to guess that better working conditions for the teachers is a big part of that discussion; whether it's small class sizes, more class room resources, more "unassigned" time that can be used for planning and/or providing individualized attention to students ... all of which positively affects student outcomes. But in the end, all of these things are working condition matters.
Though I have never worked with/for Teacher Unions, my other union experience informs me that positive and consistent working conditions make for happier, more productive employees; and happy, productive employees make for superior product outcomes (assuming management hasn't/doesn't make stupid product decisions.
I realize that many are offended with the student = product comparison; but in the end, it is what it is ... It is the job of teachers to produce the best student outcome possible, and it is the teachers' union's job to provide the best possible working conditions to promote the teachers' mission.