Why be charitable? He certainly isn't.
Because it's good practise for debate. Intentionally misinterpreting what someone says is petty and dumb.
Also common sense: If someone is a transgender woman, they aren't a grown man.
Physically, they are. Unless they've had sex reassignment surgery, in which case we should probably call them transsexual. In any case, conservatives don't agree with you.
Here's a simple question: Are you physically attracted to the physical appearance of a person - masculine or feminine?
If you're going to draw a line, why not draw it at when a person starts looking like the gender they're transitioning to? You could consider it based on attraction: If you're physically attracted to women and you're attracted to someone, is that not proof enough that they're a woman? (Or men/man, if you're attracted to men.)
That argument probably doesn't work as well if you're attracted to both genders, in which case: If a man loses his penis to accident or disease, would you not still consider him a man*? If so, wouldn't a trans-man, with a vagina instead of a penis, who looks exactly the same as the previous hypothetical man except for having a vagina, also be a man? (Example given with men because it's a lot harder to lose a vagina, afaik)
Some might claim that a post-srs trans-woman still isn't a woman because she lacks ovaries and a womb and natural cycles and so on. However, some natural-born-women lack those things as well: menopause eliminates periods w/ natural cycles of estrogen, ovarian cancer (or a high risk of it) can result in ovaries being removed (which also triggers early menopause unless HRT prevents it), and
it's possible for the womb to fail to develop.
* Yes, I know some people would consider a man who has lost his penis to be less than a man. Flip that around: Angelina Jolie has had a
double mastectomy (and then reconstructive surgery) and also had her ovaries removed - and is she not still a woman?
(P.S. Personally, I prefer to call a person whatever they want to be called, if I know what that is. Also, I specified physical attraction because it's possible to be attracted to personality regardless of the package that it is in.)