Because the second you target someone it becomes a specific threat of violence. A vague meme is different because it has ambiguity for the reasons I said. It's a dog whistle. It can mean different things to different people. Me personally I see it as attacking them at their wallets and reputation and freedom. I don't want people gunned down in the streets. I want prison. Others might mean actual violence. How you interpret it is up to you. If you need to ask every individual person what they mean, you do you, but that's a waste of time and who cares.
My stance of ACAB is if you aren't reporting the bad ones you're bad too. I'm sure there's good cops out there but you don't see them as much. Until they have consequences for their actions by removing immunity they are all potentially the enemy and you need to watch your back.
Ha! There's a name for this? This hits the nail on the head.