Humans drink human milk, and the milk of other animals. Animals drink the milk of their own species on a regular basis. I will never understand why people get hung up on this in Zootopia as if drinking the milk of other creatures OR the same species is something humans and animals don't ever do in real life. It's like y'all just want it to be weird.
Humans don't usually sell their own milk to others or turn it into processed foods; it's reserved for nursing their own babies. There are no lower animals in Zootopia, they are all anthropomorphic and behave like humans. So them having ice cream is akin to human women selling their milk for the masses to consume. It's a little strange.
I misread your reply, and I think my (slightly tweaked) version is more accurate - Don’t you know you’re supposed to dissect every single frame of a movie, so you can point out all of the insecurities it makes you feel that are vaguely relevant to the plot?
Yeah, in the same shop where they bought popsicles, an elephant was also scooping ice cream "with an ungloved trunk" as Judy points out while threatening to issue them a citation.
There's an actually quite good Netflix show version of Puss in Boots that basically no one I know has watched that makes this gag.
The barmaid of San Lorenzo is a cow, and she isn't just the (off-camera) provider of the protagonist's leche, but she held ice packs to herself to prepare milkshakes one time.
I imagine being a cow in Zootopia is quite lucrative. Not only do you produce a product people want to buy, you can also satisfy more carnal urges by allowing customers to be the ones milking you.