Given that selectivity of teacher education programs, or the lack thereof, is coming up more and more, I'd just like to remind everyone that the number of people with teaching certifications does not affect the number of teaching jobs. Everyone with a teaching certificate isn't guaranteed a job.
My understanding is that in Finland, which comes up often in this context, the government pays to train more or less the number of teachers they expect to hire.
Both systems are equally selective insofar as either way, you still need X teachers and you're going to hire the ones that seem most promising.
I'd be in favor of a Finland-like system where fewer teachers got free training via a more selective teacher education system, but I find it very difficult to believe that our current system with more stringent entry requirements would help -- unless you believe that school administrators systematically make the wrong choices in an incredibly stubborn way.