I tend to agree that teaching can clarify one's ideas, but I don't think the benefits are equal across the board. I think the argument for benefits to research are stronger when it comes to supervising graduate students and teaching seminars. I'm far less convinced that we should have math professors teaching Calc 1 if they're not really passionate about it, and I'm especially not in favor of tying up their salary and performance evaluation with it.

Note, I'm saying all of this as someone outside of academia who is passionate about science and had a very mixed bag of teachers in undergrad.