The exact same arguments could be leveled against intrapersonal utility comparisons. After all, a person's desires and tastes change over time, or even oscillate.

Not exactly, but I see what you mean. I agree that (at least seemingly) analogous arguments can be leveled against intrapersonal utility comparisons (with a similar level of inductive strength).

Of course, this makes utilitarian arguments secondary to (e.g.) democratic process. But that's the way I like it.

I would wager that you wouldn't be so pleased if your preferences differed significantly from the median voter's.