With nine states and the District of Columbia now recognizing same-sex marriages, the timing was right for the U.S. Supreme Court’s decision on Friday to consider the issue. The justices agreed to review appeals in two cases: a California lower court’s ruling striking down a ballot measure recognizing only marriages between men and women as legitimate and a separate challenge in New York state of a provision of the federal Defense of Marriage Act that denies same-sex couples federal benefits.

The high court’s decision surely reflects the nation’s shifting attitude about same-sex marriage, with recent polls showing a majority now in favor of such unions. In November, voters in three states — Maine, Maryland and Washington — approved legalizing gay marriages. At the same time, Minnesota voters rejected a proposed constitutional ban on such unions.

In 2011, Attorney General Eric Holder announced that, with President Obama’s approval, his department would no longer defend legal challenges to the Defense of Marriage Act because, among other things, several courts had determined it is unconstitutional, but would still enforce it as long as it remained on the books. There was little, if any, fallout afterward. Changing attitudes, indeed.

Still, few court observers expect a slam dunk decision that would force all states to recognize same-sex unions at this point. The ideal — and just — outcome of the court’s review would be exactly that, a ruling calling all bans on same-sex marriages as discriminatory and therefore unconstitutional, both at state and federal levels. Denying gays and lesbians the right to marry is blatant discrimination, pure and simple.

The more likely outcome, some predict, could be a split decision that addresses only the gay-marriage ban in California, without addressing the legalization or banning of same-sex marriages in other states, while simultaneously striking down the federal ban. That would require a delicate balancing act for the court, demanding some slippery-slope language to explain why it’s unconstitutional for Congress to ban gay marriage but acceptable for individual states to continue doing so. The court majority should avoid this confusing outcome.

Whatever they decide, the justices deserve a pat on the back for taking up this issue rather than continuing to ignore it. That was exactly what the high court did in avoiding challenges to bans on interracial marriages in the mid-20th Century. The court deliberately delayed considering the issue for almost two decades after the California Supreme Court struck down a law forbidding marriages between whites and “Negroes” in 1948. It wasn’t until 1967 that the justices, in Love v. Virginia, struck down so-called miscegenation laws as unconstitutional.

The pivotal justice will be Anthony Kennedy, as is often the case in this ideologically divided court. In 1996, he wrote an opinion striking down a Colorado measure that repealed gay-rights ordinances in several cities. He wrote that the repeals were “born of animosity” toward gays and that the Constitution “prohibits laws singling out a certain class of citizens for disfavored legal status or general hardships.”

In considering the gay-marriage appeals, Justice Kennedy and his colleagues need look no further than this conclusion, which concisely states exactly why bans on gay marriage should be universally declared unconstitutional. To deny any one group a right that all other groups are entitled to is discriminatory and illegal, period.