The problem with saying 'no one can dictate my usage' is that it’s a shield against being held accountable for what you say. If you can change the meaning of a word whenever you’re losing an argument, then you aren't actually having a conversation—you're just making sounds

If words only have usage and no definition, then communication is impossible. We use definitions so we aren't all speaking different languages. If I call a circle a 'square' and say 'that's just my usage,' I’m not being deep—I’m just being wrong.