I don’t think they are calling “rationalism” itself bad, but there is a fairly large contingent of people who call themselves “rationalists” who don’t show the slightest hint of self introspection or rational thought. They see everyone else as driven by sloppy or emotional thinking and completely miss that their own arguments and reasoning are sloppy or emotion driven.

The first step to being a true rationalist is to realize you’re as vulnerable to cognitive biases and emotion driven thinking as everyone else, and focus on your own thought processes first and foremost.

Being a rationalist isn’t about lording over other people, it’s about trying to make your own thought as clear and rational as possible, and that requires challenging your own deeply held beliefs and opinions constantly.

Most people I see who call themselves rationalists aren’t that.

The term "rationalism" is defined earlier in the linked comment. I don't believe it's being used with the typical definition. This quote needs context.