‘‘I can’t. It’s against my religion.’’ Americans tend to handle religious objections with care, personally and politically. When a guest says, for example, that he can’t eat the food being served because it’s not kosher or halal, the host usually hastens to find an alternative. And when people resist following a law on the basis of faith, the government and the courts may try to accommodate them. It’s an American legacy that dates back to before the founding, when some of the original colonies were set up as havens for religious dissenters. Under the banner of belief, Quakers and Mennonites in the 18th century won the right not to join state militias. The first conscientious objectors were religious objectors, and from there, the category expanded to include moral opponents of war. The same pattern holds for home-schoolers. It was an Amish father, not a hippie mother, who first got the Supreme Court’s permission to take his children out of school in 1972, based on his religious commitment to ‘‘life aloof from the world,’’ as the justices respectfully put it.

Making exceptions to the law for people of faith has become part of the American definition of religious tolerance, part of our ethos of live and let live. It has also helped keep the peace in a polyglot nation. In France, it’s illegal for a Muslim woman to wear a head scarf at a public school. In the United States, it’s illegal for a clothing store to refuse to hire a Muslim woman because she wore a head scarf to her job interview. When the Supreme Court issued that ruling last month, eight of nine justices agreed that Samantha Elauf, who lost out on a job at Abercrombie Kids because of a companywide policy banning head coverings, was asking for ‘‘favored treatment’’ — to which she was entitled by federal employment law. ‘‘This is really easy,’’ Justice Antonin Scalia said, announcing the decision from the bench.

And yet we’ve arrived at an unfortunate impasse over the meaning of religious liberty. Unlike in earlier eras, when religious objections let the faithful separate themselves from institutions they felt they could not support, many conservatives now deploy the phrase as a way of excluding other people. Take the furious outcry that erupted in response to the Supreme Court’s 5-to-4 decision to make same-sex marriage legal in every state. Conservative pushback began with the dissenting justices: Clarence Thomas warned of ‘‘potentially ruinous consequences for religious liberty.’’ Some Republican officeholders rushed to throw up whatever shield they could for people of faith. Two states have declared that county clerks may refrain from issuing marriage licenses if they don’t want to give them to gay couples as a matter of conscience. Bakers, photographers and florists — and adoption agencies and landlords — who cite their religion when refusing to serve gay couples won assurances like this one from Greg Abbott, governor of Texas: ‘‘No Texan is required by the Supreme Court’s decision to act contrary to his or her religious beliefs regarding marriage.’’

The same-sex-marriage resisters hope to capitalize on a recent expansion of religious liberties, in another big case about modern-day sexual norms. In a divisive 5-to-4 ruling last year, the Supreme Court extended to a company, and not just to individuals, the right to mount a religious objection to a law. The craft-store chain Hobby Lobby, which is owned by evangelicals, refused to pay for certain forms of birth control for its female employees, as the Affordable Care Act requires. The owners argued that providing health insurance that covered emergency contraception and IUDs offended their evangelical beliefs, saying these methods induce abortions (by taking effect after fertilization). Hobby Lobby had little scientific support for that assertion. By contrast, in defending the contraception mandate, the Obama administration could cite the consensus medical view that providing a variety of birth-control methods benefits women’s health. Nonetheless, the court sided with Hobby Lobby and its sense of conscience.