By your definition, a "man" who loses their penis in some horrific accident suddenly becomes female. And that really makes sense to you?

No, Democrats are not pushing that gender is a choice. They are clarifying that gender is one's feeling of identity, and that it doesn't always align with the apparent biology. The choice is only in whether you acknowledge and express your gender.

This ideology has been around for millennium, and is embraced by the cultures that actually look at and respect what individuals experience, rather than those cultures that come up with a framework and rules and try to impose them on everyone, regardless of whether they fit or not.