"I think this would be a good time for a beer," Franklin D. Roosevelt said upon signing a bill that made 3.2 percent lager legal, ahead of the full repeal of Prohibition. I hope Barack Obama will come up with some comparably witty remarks as he presides over the dismantling of our contemporary forms of prohibition—laws that prevent gay marriage, restrict cannabis as a Schedule I controlled substance, and ban travel to Cuba. "You may now kiss the groom," perhaps, or a version of the comment he once made about smoking pot: "I inhaled—that was the point." (Click here to follow Jacob Weisberg)

Prohibition now is different from Prohibition then. When the 18th Amendment went into effect in 1920, it was a radical social experiment challenging a custom as old as civilization. A predictable failure—the insult to individual rights, the impossibility of enforcement, the spawning of organized crime—it came to an end in 1933. Today it is a byword for futile attempts to legislate morality and remake human nature.

Our forms of prohibition are more sins of omission than commission. Rather than trying to take away longstanding rights, they're instances of conservative laws failing to keep pace with a liberalizing society. But like Prohibition in the '20s, these restrictions have become indefensible as well as impractical, and as a result are fading fast. Within 10 years, it seems a reasonable guess that Americans will travel freely to Cuba, that all states will recognize gay unions, and that few will retain criminal penalties for marijuana use by individuals. These reforms are inevitable—not because politics has changed, but because society has.

A few reference points: in April, Obama lifted restrictions on travel and remittances by Cuban-Americans. Last month the Justice Department announced that it would no longer prosecute cases involving medical marijuana. Same-sex marriages are recognized in six states and counting. In a larger frame, loosening restrictions and lax enforcement reflect evolving social norms. Gay unions have been celebrated on the New York Times weddings page since 2002. Since George W. Bush left office, American tourists no longer worry about being prosecuted for visiting Havana without a Treasury license. In L.A., you need only tell an on-site doctor at a walk-in pot emporium that you feel anxious to walk out with a legal bag of Captain Kush.

The chief reason these prohibitions are falling away is the evolving definition of the pursuit of happiness. What's driving the legalization of gay marriage is not so much the moral argument, but the pressures from couples who want to sanctify their relationships, obtain legal benefits, and raise children in a stable environment. What's advancing the decriminalization of marijuana is not just the demand for pot as medicine but the number of adults—more than 23 million in the past year, according to the most recent government survey—who use it and don't believe they should face legal jeopardy. What's bringing the change on Cuba is not the epic failure of the 49-year-old U.S. embargo, but the demand on the part of Americans who want to go there—whether to visit relatives, prospect for post-Castro business opportunities, or sip rum drinks on the beach.

For similar reasons, there isn't likely to be any retreat on the right to have an abortion or own a gun. Popular demand for an individual right is simply too powerful to overcome. The Internet has been a crucial amplifier of all such claims. With pornography and gambling, the Web itself became an irrepressible distribution tool. When it comes to gay marriage, it has accelerated the recognition of a new civil right by serving as an organizing tool and information clearinghouse. More broadly, the freest communications medium the world has ever known has raised expectations of personal liberty. In a world where everyone has his own printing press, restrictions on personal behavior become increasingly untenable.

Politicians will continue to lag, rather than lead, these changes. Republicans face a risk in resisting the new realities. If the GOP remains the party of prohibition, it will increasingly alienate libertarian leaners and the young. Democrats face a different danger in embracing cultural transformations too eagerly. Nearly four decades after George McGovern became known as the candidate of amnesty, abortion, and acid, cultural issues are still treacherous territory for them. Why get in front of change when you can follow from a safe distance and end up with the same result?

Jacob Weisberg is also the author of The Bush Tragedy and In an Uncertain World: Tough Choices from Wall Street to Washington .

© 2009