Calculus has been around for a pretty long time, there's plenty of good material out there to learn it and people who understand it to teach it, there's no real reason it shouldn't be required curriculum these days.
Even just removing one required semester (half a year) of PE and one required semester of English (which shouldn't be very controversial) frees up two semesters, which for a high school level accommodates Calculus just fine. I'd love to see mathematical analysis courses taught at the high school level too (especially since many grown adults are under the impression math in general is like the algebra they did in high school) but that might be getting ahead of ourselves.
I also don't see why you can't teach number theory et al. throughout all the math courses. I never had a formal trigonometry course because it was taught along the way.
(That sort of think has only shown up once over multiple refreshes though.)
-6 + 5 * 0 = ?
(I guess I just got lucky?)