Laws are (or should be) based on morality and morals are (or should be) utilitarian. [That should get the peasants lighting fires and grabbing pitchforks!]

Take for instance, our current laws concerning men having sex with young teenaged boys. In our culture we view this as horribly immoral but through history and up to the present day pederasty has been tolerated by various cultures and even extolled by some highly regarded philosophers. Laws against that behavior work in our society because we believe it interferes with the emotional development of youngsters and thus, find the relationship immoral. Those same laws would not work in a country that did not find pederasty and impediment to full adulthood and thus, not immoral.

Safe birth control has (in my opinion) completely undermined the utilitarian reason behind the increasingly antiquated moral codes prohibiting sexual relations between unmarried adults (in any sexual combination and in any number). The utilitarian reason behind the moral code was for the protection and nurturing of offspring and the proper support of the mothers. Before birth control, sex outside of marriage had a high probability of reproduction. Thus, there was a good reason for society insist that the prospective parents be considerate of possible outcomes. I think the prohibition in our culture concerning homosexuality is an outcome of our previous inability to offer sex as a recreation activity with no procreation. Thus, pleasure in sex was inseparable from procreation. Since homosexuals don't procreate, they don't get to have the pleasure of sex and to do so goes against the natural order.

Enter safe and reliable birth control.

All of a sudden we can have sex with no concern about procreation. This separates sex-for-pleasure from sex-for-procreation. This is not Darwin's plan. He, like God, decreed that pleasure and procreation were coupled (so to speak). But Man has (thus far) fooled God and Darwin.

It has also created a huge problem for antiquated morals -- what is the social value of a moral that has no social consequence?

Anyway, that's kind of what I think.