I often say "I don't understand..." because I'm willing to concede that sometimes my viewpoint is incorrect and I'm interested in correcting my views. Also because sometimes saying "I don't understand" is enough to get someone who holds an invalid/incorrect/unhelpful belief to restate their viewpoint clearly enough that they can see the problem with it (but of course that requires the other party to actually engage in a constructive way). And sometimes I say "I don't understand" because it's just more polite than insulting the the misinformed person.

For example, when I said "I don't understand" to your "Still just a cringey excuse..." comment, what I was really saying was "this sentence is poorly written and hard to understand, and you also clearly don't understand the context of where the term actually came from".

When I said "I don't understand" about assuming people are bad actors, I was really saying "you seem to be using the assumption of bad intent to mask your ignorance about the things you're talking about".

So now, I'll say I don't understand why you're nitpicking my use of the phrase "I don't understand" instead of responding to anything of substance I said.

By this of course I mean that it's clearly easier for you to attack my intellect than for you to self-reflect.