But in this context what we think about the legal side personally doesn't really matter. The total dismissal that you could even have a biologically defined relationship, based on sex, where the legal or even cultural element is mainly an overlay, is the problem. This idea is resoundingly dismissed, including here as we can see. Not worth thinking or talking about, bigoted. This is that inability of the left to even look at other viewpoints and try and understand where they are coming from, so they end up with a terrible myopia.
I'm in liberal wokesvile, North America, and people's viewpoints on how we define sex roles are consistently just extensions or even the very same arguments they heard about marriage equality. I just think it's incredibly naive to dismiss this, and as an explanation it goes a long way to showing why it is so difficult to reach people with what seem like obvious biological realities, and it also explains why these ideas gained traction so easily at this moment in history.
In the minds of people who have been trained in the progressive left, sex (and therefore marriage) is most fundamentally about love and attraction, which are of course subjective. Reproductive capacity is secondary to that - in fact it is barely connected for some. It resonates with well-off westerners because that's been their experience, and they've been trained for years, if they are progressives, to think in those terms.
Biologically that's not really accurate. Sex exists for reproduction, that's what it is. Love, pair bonding, etc, exist in various species like humans in order to facilitate reproduction. If we were not a sexually reproducing species we would not pair bond, in any configuration.
The difficulty is it's not that people just believe that sex is unimportant in the here and now for legal purposes for which we have marriage. They don't even accept the idea that the biological reality defines the nature of being sexed beings. They are strongly conditioned to deny that sex (the act and the role) is connected to biological functions, in case it could support the possibility of a social institution based on reproductive roles.
If they think that way about the reproductive act, then of course they will think the same way about reproductive roles like male and female. If sex isn't about reproductive capacity in a basic way, how could being a woman be about reproductive role in a basic way?
That's what you have to undermine when trying to convince someone that woman isn't a subjective role in someone's head, and it is hard going because there is probably a fair bit of unconscious effort that goes into maintaining that set of propositions, and a lot riding on it for many.