This feels like hair-splitting to me. Your comment obviously broke the site guidelines. If you'd please re-read them and do a more careful job of sticking to the rules, we'd appreciate it. Note this one, for example:

"Please respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize. Assume good faith."

https://news.ycombinator.com/newsguidelines.html

There is a big difference between saying "your argument is terrible or infantile or whatever" and saying "you are such and such", I don't think that's hair splitting at all and I also don't think that the guideline you have referenced applies in this case either, but whatever you are the moderator so there is no point in even trying to argue. I edited the problematic part out.

If you read the site guidelines closely I think you'll see that they very much do apply in cases like this. Note this one:

"When disagreeing, please reply to the argument instead of calling names. 'That is idiotic; 1 + 1 is 2, not 3' can be shortened to '1 + 1 is 2, not 3."

Not just "you are (idiotic|infantile|...)", but also "that is (idiotic|infantile|...)" is ruled out as name-calling here.

https://news.ycombinator.com/newsguidelines.html

If you want to understand why we have such rules, the key thing to consider is that the quality of your contribution has not only do with your perspective (e.g. "The reasoning is objectively infantile"), but also that of the reader—or rather the distribution of readers that your comment is probably going to land with. If you (or anyone) are interested, I wrote a long, in-depth explanation a while ago for a commenter in a similar situation: https://news.ycombinator.com/item?id=27161365. The in-depth portions are here:

https://news.ycombinator.com/item?id=27162386

https://news.ycombinator.com/item?id=27166919

Criticising somebody's behaviour as “characteristic of an infant” is very easy to read as a personal attack; I think it's best to edit it.