TBH, I don't think it was that, it's just ... a lot of the answer, despite its thoroughness, came off to me as unproductive and (for lack of a better term) condescending and unserious. The answer focused on a bunch of uncontroversial points (the questioner's later comments confirmed this, that s/he wasn't some no-gov extremist), then quickly shifted over to assuming away all the controversial stuff. That doesn't feel like it's a real attempt to untangle the issue the questioner was asking about.

At the same time, most of what you said was still relevant and true, and my disagreement does amount to an objection to your logical jumps, so it's probably an unfairly high bar I'm setting here.

With that said, I think, to address the core confusion, and contribute to the discussion, you'd need to answer "why insurance specifically"?

Yes, people insuring dangerous things is good. Yes, everyone (with a few caveats) needs to buy insurance. Yes, non-discrimination is good.

None of that gets you to "therefore, we obviously need a commission to set rates", which I think prompted the question.

As (I think) the questioner notes, everyone needs to buy food. Where's the commission that approves increases in tomato prices? I'm sure some stores would like to overcharge minority groups, but competition, and the threat of lawsuits, tends to take care of that.

A responsive (not necessarily correct) answer would look more like:

"There can't be meaningful competition in this arena, and cost of coverage is easy enough to estimate, so we've gone with a model of fixed prices."

Competition in the insurance market is pretty intense, though, so that wouldn't be a satisfying explanation.