You are right that a professional may not make a good teacher, but there is also plenty of evidence that an education degree doesn't make a good teacher either.

Of course, in a rational society where such things are not controlled by the government and special interests, good teachers--of whatever background--would tend to find and keep teaching jobs, while bad teachers would tend to lose them. Good education schools would hire out more teachers than bad ones. Just as with thousands of other vocations.

Why shouldn't a local school be able to just go out and hire somebody who can do the job? Sure, it will piss off the unions, and the educational establishment, and other entrenched interests, but I'd like to think finding the best teacher would be the goal.