ofcourse the argument, an ad hominem is an instinctive fallacy but it is still a fallacy.
a person can have little to no credibility to me, and yet say something whose logic i find flawless, and vise versa, i can be extremely biased towards someone, and still find what they have to say lacking the legitimacy of rationality.
i have to say i am positively surprised by the number of NFs answering here in adhering to the argument over the source. i always thought that the stereotypical line of thought (which i'v encountered too many times) of "if you would respect me you would agree" was basically a result of projecting a bias towards the source over the argument (thus assuming if i truly loved/respected/cared for them i should be more biased towards their logic). to me that always seems like an intellectual insecurity, as in, a lack in trust in yourself and your own capacity to examine an argument rationally, thus falling back on your trust in your capacity to examine other people's reliability.