They aren’t really thinking, per se, in that they’re forming a concrete plan with a clearly defined end goal and steps. It’s closer to the format of that common joke, “Step 1: Go out in public and denounce non-conforming people. Step 2: ??? Step 3: Profit Prophet Christian theocracy!”
There are multiple aspects to why people do this, and most of them are on the authoritarian scale, including compartmentalized thinking, assumption of widespread support due to the individual cultivating a social environment that supports their worldview, poor reasoning skills, a lack of a theory of mind and empathy with people that share his worldview (i.e. it’s so self-evident to him that he literally can’t comprehend anyone else not thinking like this), and various other aspects. But if you asked him what his goal was and what he thought it would accomplish, I would be willing to bet money that the answer would be something along the lines of “They needed to hear it,” or “I don’t know, but I needed to say it,” or other such arrangements.
