This is where it is good to use discernment and also to pray and look to God. Critical thinking means questioning everything and looking at all the possibilities. A great way to discredit a group or movement is to highlight or even "create" an "absurd" fringe and then attach that by a name or action to the bigger group so that anything said then becomes written off as unbelievable. Works both ways, of course, and we've seen it used through out history - sometimes extremely effectively