Honestly instead of focusing on beating the dead horse (especially when it was a decision forced upon them by payment processors), I would recommend focusing on bring much more attention to the topic and sharing it around. We prefer those games to still be able to exist, not nuke every site that hosts them each time payment processor comes and thinks "oh you like that NSFW title? We don't like it, remove it from the site or we will stop letting you earn money". Jam that could also focus on that issue would be also very nice way to bring some visibility.
Viewing post in Put your games in NSFW
I still think Itch is also to blame : nobody was forcing to react as fast as they did. They could have protested, made a post to warn ppl, show they searched for some other options, but it seems they just bent the knee in a flash, to worry for their safety.
(Edit : and I'm not saying they could resist, I know they can't, but they could have done things much more differently and with a hint of respect for themselves and their users.)
But in the end indeed they are not the final boss, and you should totally speak abt it and find ways to oppose this stupidity everywhere. I just don't know right now how or what could be wildly done by ppl.
In terms of if no one was forcing them to react fast - we don't know. There are already speculations they might have gotten a legal letter first, which could spearhead it way faster than Steam and as much as we can hate them going for the safe route, I wouldn't want to lose ability of my business to actually pay the bills.
In terms of what we can do - other than spreading the information and making the knowledge of the issue widespread in general population, by reaching whoever we can, we can as well try to move some law making process. Since I imagine you aren't in US or UK to sign petitions, if people would be willing someone could start EU Initative to challenge it legally speaking. If Stop Killing Games with their EU Initative could gather so many votes and might have a chance to do something with it, maybe we could try the same. Though obviously it would require way more effort than just spreading the word.