Meme-style dogwhistling actually relies on unwitting “carrier” intermediaries to spread and normalize the ideology. You see the same technique a lot with anti-trans memes too (“I Sexually Identify as an Attack Helicopter” is a common one that gets often repeated by non-transphobes).
By posting, upvoting and laughing, “normies” (emotionally secure people) play into the propagandists hands. A dogwhistle is not just the meme itself, but the entire social scenario around it. The real target of the whistle will see upvotes and laughter as reinforcement that the “unspoken ideas” espoused in it are true (there are a few in this thread).