Jesus taught us to evaluate arguments and doctrines on the basis of the lifestyle of the teachers — by their fruits ye shall know them. Gnostics want detached, abstracted arguments that can be evaluated in the pristine laboratory of the brain. Gnostics like to pretend that the ad hominem is a necessary fallacy, which means, of course, that while their argument is not “to the man,” it is rather against the Son of man, which is worse.
We should all understand the variations on this theme. The sun will rise in the east tomorrow even if a jerk today maintains loudly that it will. And someone who appears to be a very nice man can propagate damnable heresies; because Satan’s emissaries will frequently appear as ministers of righteousness, there are more than a few situations that require a second look. So there is a sense in which the ad hom can be a fallacy. And there are times when it takes more than ten minutes for the bad fruit to become manifest.
But the central fact remains; Jesus taught us that ungodliness, malice, hatred, bitterness, pride, envy, and backbiting are all forms of behavior which, when displayed, refute the carrier. The man who shrilly demands that others “deal with his arguments” instead of dealing with his obvious race-baiting, or self-importance, or whatever else, is a man who is trying to replace the fruit of the Spirit with bloodless (and therefore dead) syllogisms.