Not so sure about that. I think there's definitely some people who genuinely enjoy both making and receiving pedantic, definitional arguments. I imagine quite a few of such people probably go into mathematics which is essentially pedantry distilled into its purest logical form, form for the sake of itself unfettered to any material consequence whatsoever. Don't get me wrong, I'm not saying this as a critique of pure mathematics. For those who follow it, the stark abstractness of that fair discipline is precisely from whence springs its beauty.
But aside from pure path, I see what you mean that it can be annoying to argue with somebody who seems to see debate as a logic or word game, rather then a real issue with real consequences to people's lives and wellbeing.
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See, I have to say this is exactly the kind of rhetoric that only serves to shut down argument. Plenty of well-informed, intelligent people who are in no sense mindless groveling Trump supporters would nonetheless contest the guy is a "white supremacist" as they define it. For instance, the Slate Star Codex article I linked to you before.
Regardless of what you think of Scott Alexander (and I disagree with him on a number of issues), he is indisputably an intelligent man who does his research.