Todd, thanks for the question!
I don’t think reproductive technologies change the legal principles surrounding marriage, much, with one big exception, which I’ll get to.
Marriage is a universal human institution because every society needs to regulate the procreative consequences of male-female sexual attraction. (Marriage regulates people who aren’t married by the way, e.g. by making it clear when a baby is going to be born “out of wedlock” . . .This turns out to be quite substantively important for women, who often confuse things like cohabitation with a man’s willingness to be married to them. Marriage as a public category also lets single, as well as married people know when they are committing an act of adultery. Without clear boundaries it could be pretty hard to tell sometimes!)
So marriage as a legal status is one of the ways we get young men and women to do any one of the hard things necessary to make sure they postpone babies until they are married. Marriage is a way of wrestling with the fact that, men and women attracted to the opposite sex can just make a baby, with no intention or forethought, under the grip of a pretty powerful passion to boot: One drink too many and 9 months later, boom there’s a baby. Mom (if she doesn’t abort) is bound to be somewhere around. Dad isn’t necessarily anywhere nearby.
Reproduction via technology is never the result of male-female sexual passion. Let me put it this way: there may be a need for special laws regulating parenting around reproductive technology but they will be distinct from, and need have little to do with, the function that marriage is performing. And if we had to depend on reason and reproductive technology rather than sexual passion to produce the next generation, we’d be in trouble. I mean numberswise.
Secondly, there is an important distinction in law and public policy between encourage, permit, permit but discourage, and ban. Women are legally free to have a baby out of wedlock, too. but that doesn’t mean we no longer care whether children are born to married couples. Marriage is about trying to encourage the ideal. Like adoption, reproductive technology (in current law) is probably best seen not as normative but ameliorative—a happy answer to a less-than-ideal situation. (Some of us are enthusiastic about the former and dubious about the latter, but that’s not part of the marriage debate, particularly).
The one part of reproductive technology that I think is a direct attack on marriage, has nothing to do with technology at all: it is the decision of the law to strip some children of their legal and natural right to father, merely because the mothers in this instance do not want their child to have a father. This is the only instance in which the law permits parents to bargain away their child’s right to the support and care of a father. I can’t do it in a bar, why should I be able to do it in a medical clinic?
There’s a small but growing group of adult children of donor insemination who are getting quite vocal on this point. When the clinic points out their mom and dad signed a contract, they say “I never signed it!”