You mean if I'm a Christian. Sure. It would be balmy to believe in a fallen angel if I was an atheist, or followed other religious precepts.
Well, no. I don't see why anyone would reasonably believe that.
How, exactly. I mean, what's the purpose of this vast, generational, extraordinarily complicated (making the science of it work out) conspiracy, across countries and cultures and religious views, that makes it desirable by any of them, let alone all of them.
But once you decide the reasonable answer to that is, "Because....the devil" it's hard to find a rational way to respond. Not because of my stand on the existence of that entity but because it's doing what Christians and theists get accused of all the time, plugging God into a rational gap, into something we can't reasonably explain.
Why would Satan care if we thought the world was flat or square? If the answer is because it promotes a Godless, mechanistic view of the universe I'd remind you that most scientists across time, including the majority of its leading minds, have been among the faithful of one religious view or another, have believed in God. It isn't inherently true that to believe in measurable mechanism is to reduce or replace the miraculous.
In any event, what's the reason again for this world wide, generational, hugely expensive hoax?