> What I ultimately learned is that in a pitched political battle, people actually damage their credibility because they're afraid to cede _any_ ground to the opposition

This could be a person making a bad argument, or it could be that the individual is the opposition trying to poison the well. Cf COINTELPRO. Largely any movement has people with insane takes, and it's impossible to tell the difference between good and bad faith actors.

That, and sometimes people just aren't trying to be persuasive at all. It's extremely rare to actually see someone persuaded about anything political without enormous amount of effort, or more realistically a change in material interests.