If you want to know what would cull the teaching profession of most of these people, it would be more rigorous tests for entry into schools of education. You may have noted in interviews with these types of teachers that they aren't intelligent people. Public education would benefit from more rigorous testing of college students trying to enter the profession, period. While it would cause more shortages, the "market" would adjust and districts would be forced to offer higher salaries, mimicking how the Scandinavian countries compensate teachers. This would attract more intelligent candidates who might've chosen a different career path.