So, the history of Rule 8 is that after certain political events happened, the internet at large could not discuss them (or other following political topics) without devolving into flamewars. QQ, being for porn, decided that they did not want to spend the staff time to moderate said flamewars, which were popping up all over the place, given that political discussion is not at all the purpose of the site. Rule 1 (play nice) wasn't cutting it, so Rule 8 was born, in hopes of reducing the load.
In many ways, Rule 8 is an extension of Rule 1, so you can frame your questions in that regard: how likely would this topic be to spark a flamewar?
Rule 8 carves out recent politics as one such topic grouping that could cause said flamewars.
To answer your examples specifically, antsemitism itself probably would fall under Rule 8 due to likely sparking a flamewar due to the red hot Israel/Gaza topic. Communists and communism as long as it isn't calling out specific modern day stuff would probably be fine, as it probably wouldn't spark a flamewar.
As always, feel free to PM the staff for something more specific if you have specific story beats you want to do that might run afoul of things. We are more than willing to review and give advice.