I think the examples the paragraph gives more than backs up the statement. I’ve met people who comment out code instead of deleting it (luckily not in a long time!) and I feel the authors speak from experience here.
When I draw analogies of my past experiences to present situations, that does not mean that my past experiences are the best way to convince people of what is the right thing to do. I still need to do the hard work of pointing out what it is that is in the common interest and why eg deleting stuff and simplifying is good.
In such a discussion it won't help me to say people who disagree with me are generally just emotional, does it? Even if I may have encountered people with such emotional reactions.
I’m not going to just copy and paste the article for you. It’s literally right there.