In general what you'll find is that most of these advanced classes are dominated by certain economic groups. Public funds are advancing people with more resources when all they actually need is to pass state college entrance exams. It's not that children from low income families can't do the math, it's that they're at a huge disadvantage when their parents are often working, can't hover over them to make sure they figure it out, and can't afford Kumon. If you agree with a progressive tax rate (which not everyone does), surely you understand that this is a bad thing.
I personally think all middle and high school should be bare minimum. Kids should be able to test out of classes when appropriate. The extra funds can go toward paying competent teachers for the less advanced subjects. If some parent wants their child to be advanced, they can use their own resources to help them test out of classes and take whatever APs they need.
Also many of the comments on this topic here and on Twitter to me reek of solipsism. Every upper-class parent wants the best for their child, and every hacker thinks the story of their journey into math and CS is the most important one.