> Sorry. The damage that a bad teacher can do outweighs much or all of the good that the good teachers can do.
> If your kid would have 40 doctors throughout his life, only 2 or 3 of which were quacks, would that make you happy?
I don't think this analogy is quite right, nor is the conclusion you are using it to illustrate. A kid, especially a smart kid, knows when a bad teacher is bad and can just coast through the class (bad teachers nearly always err towards teaching too little and therefore being easy).
The worst case scenario in most subjects is they have a hole there, which in the case of non-STEM subjects is not catastrophic because they (English, history) are more about general principles rather than specific facts that nearly all adults forget. In STEM subjects, it can be worse because they build on one another.
I guess a truly bad teacher can deny evolution or something like that, but that typically only happens in controversial subjects where a student should have prior knowledge that there's a controversy. If they aren't, they will figure it out soon enough.
But really, a bad doctor can kill you. A bad teacher leaves a hole that a self-motivated person with natural curiosity can completely fill. Take programming (I'll assume you're a developer). If one of your CS profs had just not bothered to teach a specific course, would you be able to live through it? Of course, as attested by the many successful developers who are self-taught. When you grow up, you have to take responsibility for learning for yourself. If some students have to do it sooner than usual, that has pros and cons.