Atheists just got hit harder because people can just withdraw from atheist community. Knitters have harder time doing that because it's (part of?) their income. They have to play the game the way it is played.
If atheist community was to defend itself from purity spiral it would have to look something like that:
When news of sexual misconduct started popping up they should issue just one statement. "This society is about atheism. We are not in the business of promoting moral behavior. We will do everything that is required by law but nothing more. You can get molested in any large gathering of people. Atheists are not significantly more moral than average people. We can't and we won't attempt to provide you with complete safety or any illusion of it."
Unfortunately people took the bait, got uplifted and thought it's the right thing to do and that it helps them. That was the spiral. Then audience moved away because society stopped being about what they were interested in.
This article has really good observation. Parallels to pre-internet purity spirals are very interesting. Seems it could work with printing press (+direct contact in densely populated cities). It worked way better when radio was discovered. But internet makes it possible to consume any community.
The atheist movement, at that point, had spent a very long time flogging basically all religions for being overly tolerant of sexual misconduct by their leaders, and had been publicly arguing that atheists are morally superior precisely because they aren't as tolerant of things like sexual misconduct.
To then, after the movement's own leaders started getting outed for engaging in the same kinds of behavior, take an about-face on that position and say, "Whoops, guess we didn't care about morality after all," would have been many things. But, just speaking from a purely strategic perspective, since that's what I think you're trying to do, it would undoubtedly have been a spectacular own goal.
That's plenty to differentiate atheists for religions. "We report our members to police if they are suspected of sexual misconduct and cooperate fully and religions do not. Because they pretend they all are saint and we don't."
I kind of stopped paying attention after the "Dear Muslima" affair, which could be interpreted, among other things, as an attempt to move the moral goalpost. Sounds like perhaps the attempt was successful.
I'm not saying virtue signaling was never a force in the atheist community. But it seemed at the time that the thing that people were most upset about was the rampant sexual misconduct. The thing that people were second most upset about was disagreement over whether Wheaton's Law is a good idea or not. Trying to paint that whole sad, sorry mess with the same brush as this knitting Instagram situation is. . . wait for it . . . problematic.