I don't think it's so much that folks get overly upset when someone makes an honest criticism of one's candidate - I think it's more when someone is disingenuous enough to pretend to be taking a balanced look at a candidate while - in reality - actively working against that candidate.
Not only is that behavior dis-honest at it's core, but it's a bit trollish, don't you think?
My reply re "working against" was a "joke".*
* Now, evidently they accepted excuse for anything and everything. :-)