Reddit

I've had plenty of unpopular-opinion arguments here (example) and I've literally never had a post or comment removed that I know of. On reddit it happened several times from "both sides" of the traditional spectrum. I.e. the mods here are significantly less ban-happy than they were on reddit (although you'll definitely get downvoted for saying certain things depending on which community / which instance). Also, because of the smaller size and the UI differences it actually doesn't make too much difference if you get downvoted -- your stuff won't get hidden; it'll just get a sort of scarlet letter of WE DON'T LIKE THIS MAN SAYING THIS, but everyone can still read it.

Much of the Fediverse is developed by people who are pretty left-of-center, as it is based in Free, Open-Source Software, which is itself based upon left-of-center philosophy. As another commentor mentioned, you'll probably find some instances that are politically aligned with you but have been de-federated from much of the rest of the Fediverse for hate speech and encouraging terrorism.

However, as I mentioned exclusion is pretty directly in conflict with FOSS philosophies so, they are going to be small echo chambers and you might have but luck with proprietary platforms run by free speech absolutists.