The issue with the answer is less the facts and more the tone. He even uses the words "Tax rant."
It's very difficult to separate a remark of the nature of the cause and effect of the tax code from what might seem a political discussion.
The mods are in a no-win scenario. The question itself invites the results you are seeing. I would have deleted ...
I don't think it belongs, but the last time I removed subjective opinion from an answer, there was significant disagreement from many users. If it starts happening a lot, or with more extreme opinions, we'd probably take firmer action. But not every rule needs to be enforced strictly all the time.