I'm not sure if I agree or disagree. Personally, "Sweeeeeeeeet!" (Since I teach math (calculus for college credit as an adjunct professor), as well as high school math & physics.) But, I think we need to do something to attract more highly skilled, highly qualified people in science to start teaching science in schools. Unfortunately, in my opinion, this would also involve a tad bit of "controversy" - because I believe that someone who doesn't believe in evolution has absolutely no business in front of a biology classroom. Someone who doesn't believe the big bang theory has absolutely no business being in front of a physics classroom. Even in mathematics, I often question how "highly qualified" some teachers are - and I don't know the answer. If you google for math content specialty test in NY, you can find online a set of 20 sample problems of the level of difficulty that are on the actual exam. The exam (in my opinion) is a joke - it's pre-calculus level, with one simple calculus problem. Yet, there are people out there who have failed that test (or the other content specialty exams) once or more times before finally passing it. There are tons of materials you can purchase to prepare for that exam. But... it's a high school level test to see if you're qualified to teach high school math. I have students who could pass that exam during their senior year in high school. I find it scary that there are teachers out there who failed it multiple times.
Yet, just because someone aces that test, doesn't mean they're going to be that good of a teacher either. Everyone who has gone to college realizes that there are people with PhDs who are incredibly intelligent, yet can't express their material in a way that facilitates others learning it.
At the high school level, it can be as simple as the equation of the line x=4 or the line y=3. Which is a vertical line? Which is a horizontal line? (Assuming the axes are labeled x and y in the traditional orientation.) You can tell the students x=4 is the vertical line. You can hand over that piece of knowledge. But, if that's all you do, about 40% of your average students will get it wrong a week later. A month later, and it's 50/50 in the class. People think "x=4 is parallel to the x axis." Oddly, even in math teaching methods classes, they don't help much (at all) with the best methods for teaching specific concepts to kids. You just stumble around for the first couple years, with some successes & plenty of failures, while hopefully an experienced teacher will tell you, "try teaching it this way - the kids will remember." You don't have to be able to do multivariable calculus in order to get high school students successfully through an Algebra course.
So, I sometimes question just how high of a specialization GOOD teachers really need. Certainly, you need to be an absolute expert at the level you're teaching - able to work 100% of the problems without ever needing to refer to some answer key. And, you need to have enough knowledge of the math beyond so that you can refer to things the students might use something for in the future - or to prevent errors such as telling students, "here's a shortcut for dividing fractions. Multiply in a cross, or cross-multiply." NOOOooo! Please reserve the vocabulary "cross multiply" for something the kids are going to do 2 years later in algebra, thank you very much.
*egads, lunch over, or I'd go on forever on this topic.*