This seems to be an argument against hedonistic utilitarianism, but not utilitarianism in general.
It was almost certainly not supposed to argue against utilitarianism in general. It argues against the typical mind fallacy mostly; universal hedonic utilitarianism is just one particularly stupid incarnation of that, along with any other value system that arbitrarily values things valued by other minds without restraint.
This makes me angry on so many levels. (Spoilers Below)
"We believe it is the goal of every species to behave with the best ethics possible." -> Who would say that? If only intelligent beings, is the argument that every single being a utilitarian, or only a small important subset? Do we argue that apes should be utilitarians? What do they mean the "goal"; isn't the benefit of the ethics more the "goal" then the means are?
'The best ethics? It's like... trying to maximize how happy everyone is." Utilitarianism is here explained by someone who barely seems to understand utilitarianism. This is a straw man, that's not fair. Any decent enthusiast should at least provide a much more succinct response, and I imagine that in the future we should have a much better understanding of it as well.
The alien plays sarcastic in the end, saying it's "highest behavior" is "smugly tolerating inferior species". I'm curious what Zach could have put their as a realistic possible example.
Short answer, it's possible to make anything look silly when you get idiots to represent it.
Also, note that if we actually were at a point as a species where utilitarianism were the de-facto philosophy, my guess is that the world would look quite different. And I agree with Tuxedage on hedonistic utilitarianism vs. utilitarianism here.
The comic is not an argument against utilitarianism. It''s an argument against moral realism.
Zach nailed it, as usual, especially with his red-button punchline.