In general, as moderators, we try and not moderate discussion on our moderator actions for exactly the reasons you alluded to. In this case, I deleted your comment not because it was critical of another moderator's behavior, but because it was additional discussion that was not appropriate to be left as a comment. It would have been fine in meta or chat.
The ability of moderators to move comments to chat are limited (we can only do it under certain circumstances and only once per answer). The only options I had were to either leave or delete the comment. There was a "warning" prior to your comment that the discussion had been moved to chat. You also should have received a ping from a comment that ff524 left as a response (which I also deleted). I decided that if the response was insufficient, that you wanted to follow it up in meta or chat.
For completeness your comment was:
@ff524: Why did you single out two comments and not move them to chat? These weren't the only ones directly responding to the answer. Are you not thereby narrowing down the (published) range of opinions, and hence inadvertently abusing your moderator powers?
and her response was:
@Stefan I undeleted the two that seemed were correct use of comments and also highly upvoted. People interested in the range of opinions are strongly encouraged to visit that chat room.
The comments she left were one by me:
Do you have any evidence to backup your claims?
and one by a high rep user
-1: When you base your answer (even partially) on sarcasm, you lose (your) credibility and (my) respect. Your argument is that imposing some instances of "X only" inherently works against "equality (or some acceptable bounds on the proportions of) X and Y". That is clearly wrong: if things are highly skewed away from the proportions you want, you don't correct with equal proportions, you correct by skewing in the other direction. Let me ask you this: what do you think is the percentage of female speakers at the most recent International Congress of Mathematicians?
Both of these are attempting to enable the answer to be improved and not discussion. Looking at the chat transcript with the other comments, I don't see any that obviously are trying to improve the answer.