It seems to be human nature to present a looming threat on the horizon that's coming to Get Us. When I was a nipper it was acid rain, then AIDS, then the Ozone and then I really couldn't give a shit any more.
Similarly the scalability monster is what is currently stalking Bitcoinland and scoffing innocent villagers. MMM seems to have gone a bit quiet for now. China bans are currently dormant.
What do you think will be the next great disaster awaiting us?
I think Bitcoin is one of the best things ever created by "Western civilization" (Japan, China, Russia are included) ... well let's call it "Modern civilization" I hope it's clear what I mean. And Bitcoin is a harmonious part of it.
So IMO the biggest Bitcoin boogeyman would be the same Boogeyman which is for Modern civilization - the total destruction of it or replacing by something entirely different where Bitcoin along with many other pleasant to us things will have no place at all.