It is clear that there are number of posters on DP, some represented in this thread, who are uninformed, idiotic and can't reason to the end of a sentence. It is only
ad hominem to call them that
as a response to an assertion. Thus:
"You are uninformed, idiotic and can't reason to the end of a sentence" is, definitionally, an
ad hominem response, but
"Your opinion is uninformed, and idiotic and displays the inability to reason to the end of a sentence" is, technically, not
ad hominem because it is a description of the argument, not the arguer.
Is Fetterman the interlocutor in this argument? If not, then it's not an Ad Hominum.
It's actually a little subtler than that. For example, people make
ad hominem arguments about sources all the time. "Well, it's from the New York Times, so it's obviously bullshit"
is an
ad hominem argument about the NYT, having nothing to do with the merit of the substance. But, I think
for purposes of this discussion, your point is valid.
The rule in the forums is "Personal attacks", which is English for
ad hominem (against the person), is "also considered [a violation] of this rule."