This is a valid criticism of the teacher education system, in my opinion. One area which is in dire need of reform is better standards for prospective teachers. I cannot tell you how sick I got of hearing other teaching candidates in my program going on about how education was "such an easy major."
Of course, they took the easy road, got a less than impressive degree, and now many cannot find work or got substandard positions. However, I - with my advanced degree (M.S. in physics) and community college experience (I started to teach at the CC level before I was certified at the HS level) - got a damn good teaching position because I was a good candidate who didn't take the easy, slacker road.
See? Within the parameters of the public education system, the free market works
To my earlier point about lousy teacher preparation in university programs, I think that is partly the fault of education professors who foster such a lackadaisical environment. Change is really needed at that level, but I don't know how to institute it.