During online arguments, you often see people shout out “Ad Hominem” when you’re pointing out their problematic background. They assume this is a good comeback as they want you to evaluate their words in isolation. It’s difficult to understand why this is not an appropriate use of this logical fallacy, but redditor bardfinn states it very succintly:
Ad hominem is only a fallacy when someone is using it to construct an argument for the audience to dismiss what the subject is arguing, and when the personal qualities imported into the ad hominem aren’t relevant to what’s being presented. The ethos of someone presenting a subjective opinion is important to assessing how much credence to lend it, and whether they’re presenting their subjective experience in good faith
This is not a case of trying to persuade the audience that 2 + 2 = 5;
This is a case of “Yes, really, all of these parties in this discussion have ulterior motives for playing their parts in this little stage drama, and none of them are grounded in a realistic assessment of how the world actually works”.