Trans women are women, full stop. They're not cis women, but they are women, and I will treat them as such.
Why is this difficult? Yes, I came perilously close to TERFdom in college, but meeting a few transwomen and becoming friends with them and learning from them put a stop to that. A hell of a lot of the same arguments thrown at us 30-50 years ago are now being leveled at trans people, specifically transwomen.
And even at my near-TERFiest, I never felt threatened by them. At no point did the existence of transwomen make me feel less of a woman, less of a lesbian, or otherwise diminished. Yes, I have a very strong genital preference, but that's not transphobia or bigotry, and it's kind of moot anyway since I'm taken already and don't sleep around. No, I wouldn't have sex with a transwoman who still has boy bits, but that's on me, not her.
@Lilliwyt, please understand that it is actually a working legal defense in most of the US to kill someone because s/he didn't reveal being trans to you. Is that dumb and dishonest? Yes, but not a death penalty offense. Trans people are some of the most vulnerable people in the nation both a priori and because of the socioeconomic barriers that come with being so rare, mismatched, and ill-understood. Words do not directly kill, but they do contribute to keeping people in danger.
THAT is what "trans rights are human rights" means, okay? It's no different from "black lives matter." It's not saying "...and other lives/rights don't/aren't," it's "...and these rights/lives are being and have been systematically disvalued, so let's do something about that."