I'm still going to call that a UI disaster. Facebook puts "interested" and "going" in the same drop down. Can't miss it. If they did it the Facebook way, I believe a lot of the RSVP problem would go away. Now, people will still flake, of course. But we won't have the "save"ers.
Meetup uses an unlabeled, non-standard icon.
I strongly suspect that the vast majority of meetup users don't know it's there.
Just FYI: for running tech events in Silicon Valley, I expect about 50% flake rate. That's a few years ago, so there may be more bots now.