Does Free Love Promote or Impede Successful Marital Search?
On theoretical grounds, the answer is unclear. There are two obvious arguments against the modern pattern. The first is that, in a society where sex is readily available without marriage, the incentive to engage in a protracted search for a long term partner, costly in time, effort, and emotion, is much lower than in a society with more traditional mating patterns. The second is that sex, at least in humans, has emotional consequences—you feel differently about someone after sleeping with her (or him) than before. Arguably, in humans, one consequence is to reinforce emotional bonds that promote long term pairing—plausible both on subjective evidence and on obvious evolutionary grounds, given that human infants require extended care. That makes it at least plausible that the bonds forged with your fiftieth sex partner will be weaker than the ones forged with your first or second, making marital stability, when the keeper is finally found, less likely.
There are two obvious arguments in the other direction. The first is that if individuals very much desire sex and cannot get much of it outside of marriage, there is an incentive to marry in haste and repent at leisure, wed the first moderately acceptable partner willing to say yes. The second is that a successful sexual relationship makes a successful marriage more likely, so the parties are less likely to regret their choice if they try before they buy.
My question is whether anyone has produced good empirical data to tell us which side of the argument turns out to be more important. It is not enough to observe that divorce rates have gone up along with rates of non-marital sex. That might be due to other causes, most obviously easier divorce. Better evidence would be some sort of large scale longitudinal study, aimed at distinguishing the success in establishing marital (or long term non-marital) partnerships of people as a function of their prior willingness to engage in relatively casual sex. Even that, of course, has problems, since we don't have any way of creating a true controlled experiment—but an ingenious researcher might find a natural experiment that came close.