To clarify: you say that by default all PieFed instances don't even allow to link resources considered "right-wing", without an easy way to disable such anti-feature?
If so, it's basically a centralized point for censorship in a decentralized system, which is very antithetical to the spirit of the Fediverse and is something even the very left Lemmy devs prefer to avoid. I see it being very detrimental in its own right.
Shouldn't it be an offered setting instead? Like, "if you want your instance to avoid certain topics, here are filter lists to freely enable or disable"?
Much can be said about the definition of left and the way Marxists you are addressing don't see "liberal" as "left" to begin with.
What matters, though, is that you end up projecting a certain personal, even if somewhat educated, bias onto both PieFed as a project (banning right-wing outlets from even being linked to, globally), and the flagship instance (making warnings about Marxist-inclined outlets). This is very unwelcome for many, myself included, and, as previously mentioned, antithetical to what Fediverse is and what it stands for.