Eh, people believe that their side is good and the other side is bad. Also, that being bad means you are on the other side, and being good means you are on their side.
It's basic tribalism that won't be escaped by just by what they in theory believe. Also, note that most of the people aren't going to be modern leftists but just run of the mill liberal leaning independents/democrats and run of the mill conservative leaning independents/republicans. The thing is, Trump polarizes everyone (which is why he will win the primary and at best squeak out a win vs Biden, he's by far the weakest republican candidate in the general). There will be no fair trial involving him, regardless of where it's held.
I wish it were that simple, but an even remotely well-read left-wing dialectical materialist/Marxist would never dispute what LordsFire said in that post you quoted. The entirety of ideas like
base & superstructure, cultural hegemony, bourgeois morality, etc. comes down to 'capitalism & capitalists engineered concepts like individual morality, love of family, patriotism, the drive for self-improvement & hard work, etc. to generate false consciousness in the masses and suppress revolution'. The fundamental axioms of the dialectical materialist worldview inevitably and inescapably lead to power politics being their entire 'moral' foundation.
Basically, anything resembling idealism is a bourgeois spook and there is no such thing as a universal morality in the materialist worldview: in fact one's duty as a leftist (and thus a materialist by default) is to reject concepts like 'morality' and 'ethics', all creations of the bourgeois oppressor, and to focus entirely on realpolitik which puts & keeps the Left in power through whatever means you deem necessary. You can deploy whatever propaganda and justification you can think of for any particular action in that action's specific context & time, but none of it really matters - what matters is the Revolution and the only 'right' thing to do is to support the Revolution in the first place. This is, for example, why their violence is speech while your speech is violence; why Antifa will riot and howl ACAB all night but run to the cops the instant non-Antifa (not even necessarily right-wingers) fight back,
or why they decry the state and all its institutions & laws but have spent so much time infiltrating said institutions and keep the National Lawyers' Guild on retainer to help them out of any & every jam; why they'll call Catholics pedos with every breath they take and defend troons & non-trans (but also non-Catholic!) child predators alike with every other breath, and so on.
Going of their way to prosecute Trump for any reason they can think of and deploying every means they can imagine to hinder him, probably up to & including kicking him off the ballot for 2024 in every key state they can reach? (Which I believe to be the ultimate endgame of convicting him) That completely falls in line with that leftist 'realpolitik'. It might backfire, but then the same was true of the OG Antifa's antics in Weimar Germany, and they didn't let the 'maybes' and 'is this a really good idea' intrusive thoughts stop them from doing what they thought was best to serve the cause of Revolution either. What
seems like the hard but necessary and pragmatic thing to do and
actual pragmatism tend to get muddled in the eyes of ideological drones, IIRC this was what SB termed the 'hard man doing hard things' a while before that site got pozzed completely.
Tl;dr The left's morality, such as it is,
is entirely tribal. That's why calling them out for hypocrisy can really only be done for the benefit of third-party observers (to get them to realize the leftist is a savage tyrant who only desires power over them and you) and not to convince the leftist xirself that they're wrong, the often very blatant contradiction between their words and actions only constitute hypocrisy if you hold an Enlightenment/individualist moral perspective to begin with - they themselves only really care about dismantling 'capitalism' (fundamentally meaning any system they don't control) and getting the Left into power.
Yes, a 19-year-old radical activist on the college campus probably doesn't believe or even know about 90%+ of the above and think they signed on to a 'human rights and empathy' worldview, but that's why they're called 'useful idiots' and never get to run anything of importance before or after the Revolution (usually they also end up getting purged if the Left wins). The people who
do run things, like the Bill Ayers (Weatherman)-educated Barack Obama or the BLM leadership who literally described themselves as 'trained Marxists' on video, however...(Anyway, even shorter tl;dr, never ever give leftists the benefit of the doubt. If you aren't one of them, they will only ever try to destroy you.)