Equality was never intended to apply to behavior-based judgment.
Marriage laws are entirely equal — every person has the equal legal right to marry any consenting adult person of the opposite gender. All are affected equally by the law ... you may not marry someone of the same gender, someone who is not an adult, someone who is not consenting, or any animal or inanimate object.
Removing “opposite gender” in the name of equality is as absurd as removing “adult” or “person” in the name of equality (thus allowing marriage to a child or “non-person”).
SnakeDoc
I understand your point here, and agree with it, but I caution you strongly against using the term "gender" instead of "sex."
The human species exhibits sexual differentiation: a sexually functional male and female are essential to reproduction. Thee are two sexes, neither more nor less, and those sexes are readily identifiable by objective anatomical, physiological and genetic markers.
"Gender," on the other hand, is fluid and multiform: it's a social construct. Originally it was just a category of grammar (the masculine, feminine, and neuter forms of nouns and their modifiers in some languages) but now the gender activists have it meaning anything: hairstyle, employment category, affective response, dress, presentation, social role, preference, mood, style.
Don't say "gender" instead of "sex." In the present hostile rhetorical environment, to focus on "gender" is to concede all important points to the genderqueers from the outset.