As far as I can tell, censored by mods is quite rare. It's almost always for violating the site guidelines (repeatedly and/or extremely flagrantly), rather than based on the ideology of the content. Most of the "censorship" is downvoting and/or flagging from users, not from mods.

But you can post almost anything here. You want to post Marxist stuff? You can, but you need to be more than just a propagandist. Actually thoughtfully interact with opposing ideas; admit when the data is against you.

You want to support capitalism? You can do that too, but again, be more than a shill (though being a shill for capitalism is more accepted here).

You want to criticize the US? Many of us do, from time to time. But again, don't just be a propagandist or ideologue. "USA is only evil! Down with USA!" gets censored. "The United States is acting like a bully in international relations, and has a long history of doing so" is (mostly) accepted as a reasonable and accurate statement.

You want to support Hitler, Stalin, or Mao? Yeah, that's a tougher sell here. You're probably going to get downvoted to oblivion for it.