Equal treatment under the law is a right. While marriage might not be a right per se, the State prohibited from doling out rights unequally just on the basis of gender.
If a man can marry a woman (assuming the woman agrees, of course
) and a woman cannot, then the right (if marriage is a right) or privilege (if it is not) to marry a woman is not provided to both genders equally, and therefore violates the principle of equal treatment under the law.
Even if marriage is a privilege and not a fundamental right, the government is prohibited from extending this privilege unequally.
I think it's disingenuous to portray that as equality. Would you consider it to be "equality" of religion for the government to abolish your religion, but allow everyone (
you included! Don't you feel lucky?) to worship at a mosque every Saturday?