That's because it's the same argument. Both sayings are stupid, not because of the message behind them but because of their uselessness in actual conversation with anyone who might disagree. It's just circlejerking at that point, only shareable and discussable with people who already agree or know what it really is supposed to mean.

Do you know what someone who disagrees hears when I say ACAB? They hear me calling millions of people I've never met a mean name. It doesn't matter what I want it to mean. Even if I explain to them what it is supposed to mean (the conversation probably wouldn't even get that far), the fact stands that I called millions of people I've never met a mean name. And that's all anyone needs to dismiss my argument.

The whole point of these phrases is to spread the message to people who either don't care or disagree. And they are NOT effective at that very specific thing. These phrases are fine at letting people who already agree pat each other on the back though. These phrases push away the target audience.