What exactly do you mean by "marry" ?
A lot of leftist sentiments (eg trans women are women) depend on everyone kinda-sorta knowing what a word means (women) while undermining any actual or specific meaning the word could have (adult human female).
Much the same game goes on with sodomite "marriage". Marriage is supposed to be (in principle) a reproductive union. It makes sense that society would have special institutions related to reproduction. Why should those institutions be extended to sodomy?