I think you are missing the whole point with the "people who denied biology" part. People who are transgendered are not denying biology, rather they are resisting the roles that people fit into in society based on that biology.
And even that is a bit over-blown. In most cases they are not resisting those roles (arguably non-Binary people are), but rather declaring that what is between their legs should not define their role in society.
Do you actually disagree with that? Do you think that the particulars of your birth should determine your role in society? We have, as a society, already declared that we don't like nobility-by-birth, or skin color, to be the determining factor (though wealth of your parents is still a factor). And we have even declared in our laws that your national origin is off-limits there (unless you are a non-citizen... related, but different topic).
But gender, and biological sex, is the issue we started grappling with in the 1960s, and are still working our way though (not that we have skin color completely done either).
This is tough for some people to get through. They are used to biological sex determining gender (full stop), and the idea that this does not apply to everyone is tough for some. The Democratic party has decided that they will take a stand on this, like they did on Civil Rights, like they did on Gay Rights. To me it is clear that they are on the right/moral side of all of these issues.
Democrats are happy with white christian men, they are just not pandering to their fears of no longer being the group solely on top.
And to be clear: I am a straight, white man married to a white woman, with kids. I don't have a dog in any of these fights directly. But I can see the moral right of all of them, and support the fight.