Voters in North Carolina recently approved, 61 percent to 39 percent, an amendment to their state constitution that would prohibit marriage between same-sex couples. As usual with such events where supporters and opponents invoke words like “equality” and “sanctity,” the referendum — and President Barack Obama’s next-day expression of his own support for marriage equality — received immediate condemnation and approval.

Obama’s endorsement — with the words “for me personally” — implies a question at the heart of the matter on this issue: namely, whether government has an interest in limiting marriage to heterosexual couples. Supporters of same-sex marriage suggest that the Constitution says nothing about marriage; they then argue that, because of marriage’s absence in that document, that same-sex marriage should be permitted.

That position, however, fails to account for the role of federalism in a constitutional system. The U.S. government only has power to address issues of national importance: interstate commerce, monetary policy, defense and the like. State governments have plenary powers over everything else. These, their police powers, traditionally have included public health, safety, morals and order. So far, the Supreme Court has declined to rule that sexual orientation is a protected class.

The expectation of a republic, including our own, is that it will stay out of private affairs. While many restrictions on marriage, such as mental health and race, have been lifted, states still regulate marriage. They engage in social engineering, have done so since their beginning, and continue to do so in their law- and policy-making decisions. The state of Iowa, for instance, allows minors to marry only with parental consent, prohibits marriages to aunts, uncles, siblings and cousins.

Clearly, when the General Assembly enacted those provisions of law, it exercised some political judgment and discretion and acted accordingly.

Privacy and rights have little, if anything, to do with it. Most of the time, state interests are implicated. The Supreme Court rarely settles issues of privacy strictly by ruling that the government has overreached into a private area of life.

In a watershed case for the right to privacy, Griswold v. Connecticut, the Court ruled that the Constitution does not allow prohibitions on the use of contraceptives by married couples and did so by inferring a right to privacy: “Specific guarantees in the Bill of Rights have penumbras [or grey areas], formed by emanations from those guarantees that help give them life and substance. Various guarantees create zones of privacy.”

In writing that opinion for the Court, Justice Douglas commented on the nature of state powers. By declining what he described as an “invitation” to “sit as a super-legislature to determine the wisdom, need, and propriety of laws that touch economic problems, business affairs or social conditions,” he implied that states can indeed address such issues.

Even so, the fact that privacy is a fundamental constitutional right does not always control: In weighing the case, the Court upheld a previous rule of law that, to override a fundamental right, a state needs to achieve a compelling state interest by narrowly tailored means. That burden is high but not necessarily insurmountable.

Another important case, Roe v. Wade, was also decided on a hybrid basis of privacy and state interests. For that opinion, Justice Blackmun considered the rights of pregnant women and unborn children with respect to their relation to state interests when he formulated the trimester plan that we are all familiar with. In the first trimester, neither the mother’s health nor the life of the child is a compelling interest; in the second, regulations on behalf of the mother’s health reach a compelling point; and in the third trimester, the life of the child also becomes a compelling state interest.

If even reproductive liberty can be regulated based on its relation to state interests, surely marriage and family life can be as well, as it has been for centuries.

Using those cases, among others, the Supreme Court ruled in 1986 in Bowers v. Hardwick, a sodomy case, that such activity is not a fundamental constitutional right. The Court said that “any claim that [the earlier privacy cases] nevertheless stand for the proposition that any kind of private sexual conduct between consenting adults is constitutionally insulated is unsupportable.”

Further, in that case the Court noted that laws against homosexual sodomy have made it illegal “for a very long time,” that such laws are linked to prevailing notions of morality, and that those notions of morality serve as a rational basis for laws: “The law, however, is constantly based on notions of morality, and if all laws representing essentially moral choices are to be invalidated under the Due Process Clause, the courts will be very busy indeed.” In that opinion, Justice White went further: “We do not agree,” he wrote, “that majority sentiments about the morality of homosexuality should be declared inadequate.”

In a 1992 victory for homosexuals, the Supreme Court ruled in Romer v. Evans that a Colorado constitutional amendment removing protections on homosexuals as a class was unconstitutional — but only because “a law must bear a rational relationship to a legitimate governmental purpose, and Amendment 2 does not.” Put another way, “We must conclude that Amendment 2 classifies homosexuals not to further a proper legislative end but to make them unequal to everyone else. This Colorado cannot do.”

In a case from 2003, the Court overruled its earlier decision in Bowers — to an extent. Although the Court ruled that sexual intercourse between consenting adults in a private setting is an exercise of liberties accorded by the Constitution, that decision took the form of a 16-line paragraph. After stating all the state interests not implicated by the case, Justice Kennedy wrote for the Court: “The Texas statute furthers no legitimate state interest which can justify its intrusion into the personal and private life of the individual.”

Precluding the possibility of marriage says nothing about the validity of homosexuality and does not mean that homosexuals can or will be persecuted in other areas of life such as employment; housing; or political freedoms and liberties, such as jury service, voting, speech, assembly, and others that the Constitution bestows on all of us. The limitations apply to everyone, regardless of sexual preference. As with most other activities, government has imposed limits on our sphere of action based on what representatives of the people have decided is in the state’s interest.