It's a great meme. I'd say yes you are getting downvotes due to the front page effect (i.e., non-members of this community coming across it on "all" and perpetuating their denial with a downvote). I think the approval rating and # of upvotes will increase as more members of the community check Lemmy and upvote.

I do think perhaps that calling attention to the inhumane practices in cow-derived milk might rattle non-vegans more than something about meat, in that perhaps there's a recognition of a moral cost to meat but many are naively under the belief that drinking cow-derived milk isn't wildly inhumane. I suppose there's a "gotcha!" aspect to the meme that is also likely to rattle non-vegans.

I see this as a for us, by us community, and I wouldn't be worried about downvotes by non-members; but I answered because I appreciate wanting to know why posts are voted on they way they are. I'm reluctant to mention this because I don't want to perpetuate the belief that Lemmy is North America- or US-centric, but you posted at what is 6am in North America's eastern time zone. I think there are more people viewing Lemmy by Subscribed or Local during business/daytime hours and more viewing by All in the middle of the night, etc. I moderate a pretty unpopular Canadian Football community, and I've found that downvotes will predominate if I post outside of business hours/during the night; that - combined with my own Lemmy habits - is what most of my reasoning above is based on. I predict this post will have net 15 upvotes a day from now :)