I doubt the book is about punching near centenarians who were members of a specific political party in the 1930s and 1940s. "Nazi" is now colloquially used as a general term to describe fascists and bigots.
Here is the Merriam-Webster definition for the word[1]. The traditional definition is definition 1. The definition the book is using is definition 2.
You don't need to wear a swastika to be fairly categorized as a Nazi according to that second definition. Some people espouse Nazi and Nazi-like ideals without self-identifying as Nazis. That seems to be the underlying meaning of the above passage.
Given that most conservatives hold positions that are perceived by the nazi punching crowd as one or more of those evil stances above, I feel like the concern is genuine. Emphasis on perceived, because there is a tendency to exaggerate just how "anti" such stances are.
And there's the issue, front and center. If someone like me is worried that labels are getting thrown around in a wanton and haphazard manner, and such labels are used as justification for violence, why is it seen as a character flaw for me to worry that such labels might be foisted upon myself in the future?
>"only to immediately think "they are talking about me" that is a problem on your end."
Honestly, part of why I'm so concerned is that I can't read this as anything other than an insinuation.