For lots of people, "marriage" is extremely intertwined with religious practice, and some religious traditions don't recognize same-sex marriages. It's not a m

For lots of people, "marriage" is extremely intertwined with religious practice, and some religious traditions don't recognize same-sex marriages. It's not a matter of a specific desire to discriminate; for these people, marriage simply isn't a thing two men or two women can do. Furthermore, for the separate population of radical people on the left, they tend to be skeptical of the role of the state in shaping domestic relationships and structures, so they tend to advocate for the abolition of legal structures (like marriage) that privilege certain types of domestic relationships over others. You can even see this in the history of the LGBT movement in the United States -- before the 1980s and the AIDS crisis, LGBT activists fought far more often for the abolition of marriage, not for gay marriage.