The "Is it good for us? Let me modify my interpretation/beliefs" act you're describing is in itself rationalizing. What you're focusing on is their motivation for doing so. And yes, it is a simple motivation.
You are right that there is no reasoning with radical groups like MAGA/QAnon/mainstream conservatives. We cannot pull them out of their extremism with reason. They have to want to change themselves.
Trying to persuade family who have fallen into this extremism typically backfires and results in frustration, anger, and hostility. This tends to just push the family member(s) further into the community they feel "gets them."
All of this is cited and elaborated on in this blog post of mine. (I have ads turned off and do not benefit in any way from my blog.)