Once a marriage is legally defined as being anything other than one man and one woman, there does not exist any legal framework to deny any other combination of genders, persons, and species from entering into a “marriage”.
That is because the standard for having a marriage becomes whatever someone define as love or what makes them happy.
Who can define that for another person?
One the legal standard of one man and one woman equals a marriage is breached, there can be no standard. Every possible standard, ie a marriage is only between two people, two humans, etc, can be successfully challenged and overturned.
This is the red line that society cannot cross without irreversible and unintended consequences.
And it is not up to 3% of the population to dictate to the rest of us what our standard of marriage is to be.
The goal was always simply the destruction of marriage.
Not quite, a legislature could define marriage as something else and then it would not open all those doors. What opens all those doors is a court deciding that marriage is a right.
Once something becomes a right, then it belongs to everyone. A legislature redefining marriage would keep it still limited, but less limited than in the past.