Cults aren't nessecarily a bad thing, despite the connotation. It's good for people to come together and support something they feel strongly about. It's only when people use these tactics to manipulate others where the problems lie.
Religion and spirituality is an important part of human society that has existed for thousands of years, and it gives many a sense of belonging and community. I can tell that you probably didn't grow up in a religious household. Neither did I, and while I don't subscribe to any religions, I atleast can understand.
Dude got killed because he tried to spread his religion to the wrong island. I completely get it, but I just think the victim blaming is excessive.