I always got the vibe that the scorn was for people who were doing it just to look good but didn't actually care or were fairweather friends. Like, if you're an ally you should be doing it because it's right, not going around bragging about how good you are to those poor, benighted trans people.

On the other hand sometimes people take it a bit far and are dismissive like you say, which I can get, i understand it, I don't think anyone should be too broken up about it. But it does suck to feel like you're trying to do the right thing for someone even though they seem not to really like you very much.

It's complicated I think. It's good to express appreciation for people being with you, but at the same time you don't want to feel like someone is lording something over you.