Don’t bother looking for justifications. They are infinite, because they are not honest. If their side does it, they’re in favor of it, no matter what they do.

It’s best to point out that this is what’s going on, that many others don’t do this, and after people read your comment, they’re left seeing the truth of the soulless, valuelessness of that behavior. It’ll make people slightly less likely to do it each time this repeats.