Present-day racism and slavery are in completely different neighborhoods of magnitude; to the extent that the comparison borders on false equivalency.
>...the new moderation changes allow statements like "Immigrants are grubby, filthy pieces of shit."
If a platform is attempting to operate within the ethos/spirit of free speech, you 'should' be allowed to make such statements on the platform. The root of the argument is the disagreement on whether and where one should be "allowed" to say those things.
Saying it's problematic is not a trump card (no pun intended). If you can demonstrate how allowing people to say offensive/harmful things (excluding established limits on free speech regarding safety) is inconsistent with free speech, then you're adding something to the discussion. Anything else is likely a disagreement on utility of free speech vs. civility; a place where folks can agree to disagree.
Ah, but you aren't allowed to say "Christian men are totally useless" or "Lesbians are so stupid", so it sounds like you should take up the ethos/spirit of free speech with Meta as well.