I get the need to being able to identify and by part of the group, but when I meet someone, I don't care. They identify as male? They are a man. They identify as female? They are a woman. Clearly that is how they want to be perceived so I will treat them as such. But when such person goes and tell everyone "Hey! I had a male/female body before it! Just so you know!" It is like they want to be perceived this way. Not just male or female, but like some third gender or something. Also w/e you like it or not, there is a lot stuff that you will be thinking unconsciously once you learn "the truth" and even most tolerant people can have slips or won't be able too see them as 100% the gender they want to be because of that.
Sure, they might want pat on the head for all their hard work, but isn't that what friends and/or family are for? For total stranger all it does its making them feel as if you are playing sympathy card in order to show them how much you went through. It would only make people either afraid to say something wrong and tiptop around you or they wouldn't care and maybe even start to say/ask really unpleasant thing. I will just never understand it. If they went all the trouble to be able to express themself and be perceived the way they feel is right, why would they then ruin it by going and telling everyone about their "sad past".
Some people haven't fully transitioned yet. Others never will. For those people, it'd make sense to clarify by saying they're trans.
Some will have struggled for years to figure out who they are. If it's such an important part of their identity, they may want to express it freely which doesn't mean they'll tell everyone, especially strangers. Even if they do, all they're saying is that they were born in a body that didn't line up with their gender. It doesn't imply a third gender, but it's still very unusual.
Hence it's fine to have a lot of subconscious thoughts about it as long as long as you still treat them as equals. They probably have thought about it more than you.
I doubt they're asking for a pat on the head. It's about acknowledgement and whether you accept them anyway.
Some may not have friends or family (anymore). In that case, I dare say they deserve sympathy (which they aren't entitled to but it's nice if they get some). If people are afraid to say something wrong or tiptoe around the subject or start saying or asking unpleasant things, it is because they're uninformed or even ignorant which is hardly the trans person's fault.
You say you'll never understand it and that leads to you arguing against your own impressions and reactions. You argue against a hypothetical trans person who's so aggressive with their identity to the point that they yell at strangers. You argue against implications that you read into it and weren't necessarily made by Uranusmyname'stoolong.
All it "ruins" is your personal perception.