That's because they hold to a Calvinistic morality. They and their flock are the Elect, and everyone else is a hell-bound reprobate. If you go against MHFM, you are going against God. Just like Calvin when he ran Geneva.
Well put, their viewpoint always struck me as being some sort of neo-Calvinist view regarding the elect. They do come across as cultish, especially if you read the comments on their videos and online posts from their followers. I like a lot of their content (especially since their material got me started on my journey to Catholicism), but sadly they are not without issues.