People are joining federated Reddit alternatives because of the sorry state Reddit is in, so most users here are ex-Redditors (myself included, but I quit Reddit a long time before Lemmy launched). Anyone familiar with Reddit knows that the userbase is politically diverse, and that there are plenty of unhinged shitheads.
Lemmy’s core developers are openly Communist, and run lemmy.ml and lemmygrad.ml. I may not be on the same page politically with them but I’m not dropping my support for the platform over it. If anything, I like the idea of Communism as a philosophy for running an Internet community moreso than I would for governing a nation. Though there are plenty of people who consider Communist ideas of any kind to be a dealbreaker and join Kbin and Mbin instances as a result.
Anti-communists do tend to trend towards reactionary politics, so you end up seeing that kind of thing a lot more from non-Lemmy instances. Similarly to how conservative-leaning users choose Pleroma et al over Mastodon, since antifascism is a core philosophy of Mastodon’s mission (being a German nonprofit and all).
Though the far-left users on Lemmy do also tend to adopt a reactionary anti-Biden stance, but definitely not for the same reasons.