It's not rhetorical and it is not literal either. A rephrase can be "what you are saying makes no sense for the reasons I am about to lay out and I would like it if you can address my points below, based on my understanding the argumets you made lack basic coherency, please tell me what you think of my counter-argument".
If this was a work email in a super-uptight place I would say something like that. Had I known that simple phrase I use all the time would be so controversial I would have avoided it or rephrased.
You chose to question my motives and assume the likely explanation is that I am atracking the person instead of their are argument. I am insinuating that their argument sounds ridiculous but I am not implying that as a fault of their intellect or personality but a lack of perspective where sharing my perspective might help them change an opinion.
I will not defend my personality and motives being questioned when I made no attempt to do so, I also did not the attack the person themselves in anyway. You should not assume malice. I think @dang saw me break rules in the past over one of the politcally charged threads and assumed it was in my personality. Feel free to review my post history on technical topics like this, I make best effort to avoid ad-hominem or anything resembling an insult. Presumption of malice itself is unfair.
I have nothing to gain by attacking anyone. And even if I did, you should look at the context od what I said after that phrase to find out what my intent was. If I don't promote myself or say anything against the person why are you assuming malice?
What about when I said "please try some threat modeling here" is that being snarky as well? It can be if you assume malice. I hope no such assumptions are made.
Either way, I did make a mistake: after years on HN, I keep forgeting that it is to be treates like a corporate/work environment. Two friends using my ever so controversial phrase would not assume malice or police for snarkiness, but two coworkers or paries of a business meeting/engagement would.
I will be careful to be more aware of the environment.
Oh, and not all discourse is interpersonal. It is done interpersonally but the subject of the discourse is does not have to be the other party themselves,their intellect or character (and was not the case in my response -- very obviously)