I don't understand where folks get the idea that monogamy and marriage have somehow become a thing of the past.
I'll hear folks using divorce rates, for example, to make the case, without realizing that many divorced people remarry. I know people who have been married 3 or 4 times. The institution is as popular as ever, as near as I can tell.
Hell, I've been married twice, the first time for 19 years (separated after 18 years), and the second time for 12 years and counting.
Serial monogamy counts as evidence against monogamy? I don't think so. Just the opposite, in fact.
I don't know about anybody else, but I've seen folks all across this nation (and indeed all around the world) struggling for the right to marry. Maybe they didn't get the memo about the end of marriage and monogamy?