The thing is, it is so much work to teach and to stay a teacher, that the lazy, poor performers usually wash out quickly. They have to accomplish a number of difficult tasks, from getting a college degree, to a massive license test, to peer reviews, and supervised classroom time before getting that full qualification. Most teachers do not graduate with a regular license. It takes years after college to earn one. You can't fake your way through any of those steps, so the rigorous process tends to weed out a vast majority of the bad teachers. Not all, but most.
Point #5: Conservative hypocrisy. This last bit is my current personal beef, though Jon Stewart has echoed a number of my sentiments on his program. I guess he isn't echoing me, per se, but anyway; Republicans who recently threw a royal fit when couples earning over $250K a year might have their tax cuts expire are some of the same ones now claiming that teachers make too much. They say it is tearing away freedoms if we try to regulate the financial industry or put ceilings on bonuses (in the millions of dollars), but $50K and some health care is too much when it comes to teachers. As for the argument that the public's taxes pay for teachers, but not those said financial people, after the major bailouts of the last few years, that is simply not true.
Wall Street got us into this mess, but the Republican party wants to make civil servants, like teachers, pay to get us out. What's more, teachers are willing to make sacrifices, unlike the aforementioned Wall Street workers, but GOP governors want to take away their union bargaining power anyway. It took a long time for teachers to earn a decent wage. How long will that last once they no longer can collectively bargain? The Wisconsin and Ohio fiascoes currently in progress are a total stain on our nation.
Wrap up: On a broader scale, is it democratic to limit pay, or are we just trying to transfer the wealth, stealing from the rich to give to the poor? The heads of companies now often make one hundred and eighty times what their average employee makes, versus more like forty times as much in the past. These are estimates, but ones in the ballpark with reality. I do not think it is unreasonable to expect employers to pay employees more when we are talking about those kinds of disparities.