Bigots can’t rationalize their bigotry. At least not in a way that can’t be torn apart. They always end up using circular logic, which is what the comic is address.
I’m “offended” at racism because it creates an unsafe culture for everyone involved. I can cit research about the effects of generational racism leading to higher crime for instance.
They’re offended at the sight of black people being able to use the same water fountain as them. They can’t tell me why, which is why their argument ends at their “offense” and is the scenario the comic is about.
Also, it’s never just “butts”
I’ve seen people online get offended at the bumper sticker “Fuck Cancer”.