Pinging
@Theglassman12 due to also being relevant to this
The distinction here doesn't change the point of my analogy. If it would be rude to use against the person, don't use it against the argument. There are other ways of getting your point across.
I completely disagree with this, think it's a terrible route to go down, and know that it goes completely against our precedent for what we punish for. Which is particularly relevant since LordGinSama's a fairly long-time user.
On why it's bad, well, I think my response here is a fair enough example. Should I not be allowed to call your suggestion "terrible", since that'd be a rude thing to say against a person? Oftentimes arguments genuinely need to be described in ways that, even at their nicest, would be considered insults if applied to people, such as "illogical" and "unreasonable". While these can upset people, I think that's the price we have to pay to be able to talk about some things.
You can fairly easily argue that "shit" or "braindead" are worse, but to draw a line you'd have to draw one right in the middle; where some people will be offended by unpunished speech, and some people will casually toss out punishable speech without a second thought, which I think is generally a bad situation to be in.