the "private company" argument doesn't apply super well when there are only a handful of options and they all have the same political ideology.
https://www.theatlantic.com/technology/archive/2012/03/cours...
"We always remove images of explicit sexual activity or fetishes, and nude or partially nude people in sexually suggestive poses."
Does GabTV have anything like this in their terms of service? Answer: No. They signed up with Stripe, agreed to the ToS, and now are generating moral outrage when Stripe comes knocking.
This is a true fact. But it is completely unrelated to your previous point, about slippery slopes.
This very much does seem to be a slope that is quite slippery.
Yes, a couple psuedo oligopoly payments processors could indeed collude together, and ban whatever the controversial thing of the day is.
This would be perfectly legal and the fact that it is perfectly legal and easy says something about our society. It says that the metaphor of a slippery slope where more and more people get censored, because they were on the wrong side of a corporation, is an accurate analogy.
But that's not what's happening here. Stripe has a very specific rule that gab.ai agreed to when they signed up. That is, no porn. Every company that uses Stripe that I've found includes some blurb in their ToS referencing "No Porn Allowed." I've also found it very difficult to find porn on these platforms using some generic search terms.
Of course gab.ai wouldn't want to do include this in their ToS, since they bill themselves as "champions free speech, [and] individual liberty". So now when Stripe comes to their front door asking about that thing they agreed to, now they are whipping up everyone into a moral outrage of "we are losing our free speech!"
Don't fall for it. Yes, those who control the purse strings control the speech, and yes payment processors who allow porn are very very limited and outrageously expensive. But from my experience in webhosting, this is very much tied to the fraud associated with the domain. If they don't like it, they can integrate with a payment gateway and merchant account themselves instead of using a full stack payment processor.
So many commenters on this are jumping to a slippery slope fallacy as if Stripe has any moral imperative to uphold free speech. They are a private company and have their own reasons to disassociate from any client they wish. That is their prerogative, and as long as they are not discriminating against anything that is a federally protected class (and last I checked, hosting porn is not federally protected) they can cut off services to anyone.