Not an unpopular opinion. Milk has been, is, and likely always will be a common drink with or without food.
You might find some niche quibbling over whether or not it's better than any given drink with specific dishes, but that's not the same thing as your argument in the post image.
Is the context significant for UnpopularOpinion? Because I feel as if you posted pro-Trump fascism here, you'd get upvoted as being a truly unpopular opinion, but if you did the same 70 miles N of Minneapolis, you'd be quite popular.
Lemmy is left-leaning, and vegetarian-leaning to a lesser extent, so I'd say OP's opinion is probably unpopular on Lemmy. If we're taking nationally, then sure, it's not an unpopular opinion, but most of these are evaluated in the context of Lemmy. Not Twitter, not Reddit, not Fox News.
Now, if you disagree with me about the veg-bent, that's another thing. Maybe it's just my local server amplifying those voices, and I'm wrong about the larger Lemmy zeitgeist.
Eh, this version isn't too far from the reddit one where you get plenty of "disagree/agree" votes instead of voting on whether or not it's unpopular and thus appropriate as a post.
But, no, I was working from the broader perspective, which is what the premise is supposed to be about. I get you, though. On lemmy, the opinion is more unpopular than it would be in general, or I think it would be. No way to verify that. All I can do when casting my vote and commenting about why I made the choice is from my direct experience on almost any subject because nobody is going to be up to date on everything on a professional scale where they can be authorities on the topic. Most people, myself included, would be lucky to have even one area where they could state for certain that a given opinion is popular or not everywhere. I sure don't.
But you can, usually, vote based purely on exposure to the topic and be in good faith as long as you expose yourself to the topic wide enough to matter.
Besides, on my end, I was taking the image contents more as a whole. The opinion seemed to be about milk being perfect with any given dish, much like a wine pairing. I did assume the perfect part was rage bait, and ignored that hyperbole.
Since I have seen people order (or try to order) milk with a wide range of cuisines, and know a lot of people in my local area that do drink milk with most meals (and that's adults, not kids) at home, that's where my opinion about the post came from.