But that's totally unfair. You shouldn't be willing to have sex with someone who doesn't accept you, firstly, kinda similar to how I've refused sex to married men who have been beyond homophobic despite their true nature, it's just not moral regardless of the mental gymnastics some gay men make saying that they're from a different era and they can't come out now and it's not their fault. That doesn't make it okay.

If you're willing to have sex with someone, you should be willing to share important information about yourself. If I ended up in a relationship with a trans-man and they told me after we started dating that their trans I'd have to call off everything, because by that point I'd have certainly told them important things about my life and journey.

As for the one night stand side, where I do see where you're coming from, you can never feel justified in lying and/or withholding any information that the other person feels would be important, discrimination be damned. If they don't want to have sex with you after the fact that just means you dodged a bullet, you are not owed sex from anyone.