Ok, Mastodon is officially a lot more awesome than I had realised. There's a federated server for everyone who's really into bitcoin, and, yes, it is full of people who are as awful as you can imagine. But, with one click, you can block the entire domain! 12.8k thousand crypto weirdos filtered out in a click. Amazing.
even better: being on an instance where a) they don't tolerate sign-ups from folks like that b) they tend to block those sites before you even think of picking up the Whack-a-Mole club