Discussion on tenure

This semester, I have been constantly frustrated with my classes, teachers, and the educational process in general. It becomes more frustrating when I remember that my DREAM is to be another tool in this educational machine that seems to be beating me down every day. However, the dream never fades, so I know this is really what I want.
Still, I try to define and identify my frustrations instead of just getting angry about my busy schedule. Right now, I think an issue of interest to me is tenure. Discussion on charter schools has sparked conversations about the sanctity of unions. Should teachers be unionized? Do unions do more to protect teachers or to protect students? I really want to understand this before I dive head first into the teaching world.
And article (http://www.theatlantic.com/business/archive/2013/09/study-tenured-professors-make-worse-teachers/279480/) cites a study performed by Northwestern that took into question the quality of teachers under tenure in comparison to those without tenure. The study concluded that  "Professionals who are paid entirely to teach, in fact, make for better teachers." 
I think this is important to consider in this discussion on education in society. We talk so much about teachers being evaluated, but I think instead of placing an emphasis on tenure, we should look more at the quality of a teacher. As this study shows, teachers who are not protected by tenure tend to be better teachers! If this is also true in public schools, as I imagine it is, then by removing or limiting tenure, we would be protecting the quality of education our students are receiving.