When someone says, "Hey, I prefer X for myself", I generally make an token effort to acknowledge and accommodate that preference because it seems like the sort of thing a decent human being does.

Right, but no one actually said to great_kraken, "I'd prefer it if you to say 'transgender' to 'transgendered'."

You just went full speech police because you felt so empowered. And what I'm telling you is that your dismissive attempt to shutdown discourse in the way you did is toxic.