Even if there are people who would endorse the comment, that is not what the person leaving the comment is likely going to be "feeling" in that moment: they are reading a bunch of comments that they are bothered by--ones which none of the other people around seem to be taking serious issue with (which is a key part of the original problem statement)--and those are the people they are going to perceive as being the ones who must endorse their comment: the ones to whom they are effectively submitting themselves for "endorsement".
(Which, frankly, I think is a separate reason why this endorsement system doesn't make sense as a solution to an endemic problem: most of those issuematic threads are filled with users--many of which have high karma--who are reinforcing the negative comments; it is unclear to me why the negative comments aren't going to have an easy time getting endorsements given that they currently don't have a difficult time getting upvotes.)
I thereby feel like even if this feature "worked" (and again, it isn't really clear to me why this would help, given that it isn't like these users are currently being downvoted or flagged out of the conversation) it still might not be an "appropriate" way to solve these underlying problems (which I would claim are inherently messy and emotional).