It was an argument about whether something is taboo. Taboo is a measure of popularity. He says posting an ad for your personal venture in the signature is in bad form, the vast majority on the forum say it doesn't bother them. Therefore, in the "culture" of this forum, there is no taboo against it. Argument from popularity is perfectly valid, because popular opinion defines a cultural taboo.
So, when you're losing that battle, the standard apologetic tactic is to shift the argument to whether or not you're allowed to have a different opinion from the culture. Which, of course, most people would agree that you do have that right. This is a weak attempt to make it look like you won the argument.