The legalization of same-sex marriage in Maine has had none of the negative effects opponents warned about before the historic vote nearly two years ago. Traditional marriage has not been diminished. School curricula have not been changed. The courts have not been plugged with lawsuits.

No, the real impact of the law has been overwhelmingly positive, particularly for the thousands of couples who can go about their lives secure in the knowledge that they are protected under the law.

But despite the steady rise in acceptance of same-sex marriage across the country, millions of gay and lesbian couples are still denied adequate legal protection. The Supreme Court, which will decide this week whether to consider a number of same-sex marriage cases for this session, should act now to declare marriage equality a federal constitutional right.

The marriage equality movement has been building toward this moment for years. Since Massachusetts became the first state to recognize same-sex marriage in 2003, 18 other states have followed, through popular referenda, court decisions and legislative actions.

Maine joined that group in November 2012, the same night voters in Maryland, Minnesota and Washington state also legalized same-sex marriage.

Fifteen months ago, the Supreme Court struck down the federal Defense of Marriage Act, which defined marriage as between a man and a woman. That forced the federal government to recognize same-sex couples married in states where their marriage is legal.

Now, a series of lower court rulings have used that decision to strike down same-sex marriage bans in five different states. In fact, until a federal court upheld Louisiana’s state ban last week, judges had ruled in favor of same-sex marriage advocates in 20 consecutive decisions since the Supreme Court decision.

It is clear where this is headed. One by one, or a few at a time, the state bans will be struck down, until same-sex marriage is allowed and recognized throughout the United States.

But that could take years of costly legal wrangling in the most reluctant states, where acceptance of gay and lesbian rights in general and marriage equality in particular have lagged behind the rest of the country.

Meanwhile, loving couples in those states would continue to live without the stability and security, not to mention the dignity, that marriage affords.

That is unnecessary when the legal and moral imperative for same-sex marriage has been so plainly demonstrated, and it is absurd to leave the state bans still intact in some sort of legal limbo.

The Supreme Court should settle this matter, and settle it now.