Agreeing with /u/Alyssa_B. Putting an ethical obligation to disclose on trans people harms trans people. It means that in every relationship we attempt, we'd have to dredge up our grief, anger and pain and put it out there for another person to judge. It means we can't put our past behind us and move on with the new lives we've worked SO HARD to get. It would change the dynamic of a relationship even if the other person wasn't transphobic and didn't reject us. It would put us in their debt for "giving us a chance," and it would change the way they looked at us. I think it's very hard for cis people to view us as we want to be seen. Once they know, every part of our appearance, everything we do, they see in light of our trans history. That corner on my jaw isn't just my normal, pretty face, it's because I was a man! Once they understand it they can't forget it, even with the best intentions.

edit I forgot to say, I think the one and only reason we might be ethically required not to live in stealth is for the sake of other trans people. So if they're questioning their gender they can meet you and have your story and your strength to counter the messages they get from cisnormative culture, that being trans is doom, "man in a dress," etc. Speaking from my own life, I would have started on transition YEARS ago if I had known about it. I had never met a trans person, nobody explained (correctly) what transgenderism and dysphoria were. I had dysphoria but no words with which to explain it.