Oh I know, but there is some things that are objectively evil, like killing children. And since their god is omnibenevolent and all knowing, then there is no point in killing children, unless your god is either evil or not omnibenevolent, you can’t have both.
But yeah, there are things you just have to accept that these extremists just take for granted, like they are so chosen/special that they can have the cake and eat it.