Why would I accept that there's this doomsday barreling towards us at high speed, and the only way to avoid it is economic devastation and serfdom for my grandchildren?

That sounds an awful lot like a long con.

Most rational people have arrived at the very reasonable conclusion that the more extreme the danger is, the more justified we are in attempting cutting edge countermeasures. So when the response we get back is "oh no, you can't do that, anything but that!"... the more it sounds like it was a grift all along.

This requires no conspiracy, by the way. Large groups of people can subconsciously coordinate in these ways without even realizing their doing it. Just takes a bit of groupthink and a small dab of neuroticism.