I wouldn't go so far as calling those people leftists (same as tankies aren't leftists) but "math is racist" is definitely a thing that happens. People were suing in Canada that the tests to become accredited as teacher includes maths tests, and because some statistic somewhere showed that black folks score statistically lower on maths, they claimed that the requirement to pass it is racist. That completely ignored that they could re-take the test as often as they pleased and that plenty of education was given to prospective teachers that enabled them to pass those tests. A lower court agreed with the claim of racial discrimination, the constitutional court then struck it down pretty much saying "lulwut" in legalese.

No, maths is not racist. The people claiming it is racist were the racists here, thinking that being black makes you somehow inherently incapable of passing those tests, so much that you can't even pass them with studying. Also I bet the disparity in maths scores by skin colour vanishes if you control for socio-economic status but the complainants would've needed maths to understand that so they didn't.

OTOH, optically those kinds of fucks are associated with leftism and I'd say it's important to openly respond to that kind of silliness with "lulwut" before the courts get around to doing it.

As to black lives matter: I think it was a strategic mistake to oppose "all lives matter". The slogan, that is, not the racist fucks. Instead, it should've immediately been appropriated by the movement precisely to define it and to leave no doubt in anyone's mind that you don't mean "non-black lives don't matter", which is understandably a reading lots of people had because they're projecting their own racism, or just racist realism.

“Sure, I’m cool with trans people (maybe I’m even trans myself), but neopronouns are where I draw the line”

Neopronouns are an enby thing, not trans and yes I'm completely fine with calling you they/them and have no issues with your ingroup using as many different pronouns as there are members, but I'm not going to fucking remember all of them. I very much draw a hard, red, line at "difficult on purpose" as that would validate people's vulnerable narcissism, "prove that you don't hate me by jumping over random hoops I come up with". Leftism is not the defence of maladaptive personality traits.