Sea Cow said:
I suppose this could be quantified. Find the number of marriages that had been illegal as a percentage of total marriages. Multiply this by twice the number of marriages in states where this had been illegal. This is the number of affected people.
You could go further, summing this over the years -- although this would probably overstate the effect somewhat, since I imagine the increase of such marriages has more to do with the change in culture than the change in laws (and in any case, seems to have more than nothing to do with the change in culture).
You could also take it a different direction by computing the change in welfare. Presumably, some chose to marry another (suboptimal) person, decreasing their welfare; some chose to live with the person they could not marry, losing the legal benefits of marriage; and some chose to move to a place allowing such marriages. Assuming that people chose the best course of action for themselves, and with some appropriate (Chicago-school) measure of the first case, taking the minimum of the three across some distribution of preferences for the number of affected people would give a rough estimation of the monetary equivalent of the loss suffered.
Let's say that in all cases, option #2 is best (stay with the person, but don't marry). If the number of such marriages would be about 50,000 per year (for a total of perhaps a million such marriages at any given time), and 3% of those were made illegal, and the lost legal benefits of marriage were $10,000 per year, then that's a loss of $10 billion dollars per year. Of course the societal (dead weight) loss may be less, as some of that is recouped (wrongly) by the government. But I imagine most of the loss would be real, and only a small portion would be transferred to the government in fees and taxes.
But, even assuming my calculations are reasonable, that doesn't say whether it's an overstatement or not -- it would just reduce that to a question of whether $10 billion is a lot of money.