They make other people's lives miserable because their leader is insane, and all of the followers are too deeply brainwashed to think otherwise. This group isn't anything new, they've been around for a very long time, and this video is probably the least of their terrible actions. Mathew Sheppard? They protested his funeral, and they've been trying to build a statue commemorating his time in hell.
Anytime a family member rejects their beliefs, they're quickly expelled from the family and never spoken to again.
However, even with all of this, we shouldn't care a damn. Every time you get riled up about this, you're giving them attention. You're making their cause more wildly known, and you're attracting a new member or two to their group.
Ignore them. They have every right to say what they want, no matter how insane. If they ever step over that line, they can be arrested. Until then, just forget about them. They have no real power, their movement is universally hated, and their group is the punchline to so many jokes.
Just take solace in the fact that you're more well liked than the entire group combined, and that you'll live to see the day the leader dies of a painful, old person related illness.