ARIZONA’S LEADERS have again pushed the state into a roiling national debate, and on the wrong side. By the end of the week, Gov. Jan Brewer (R) must decide whether to sign or veto a bill that would enshrine the ability of businesses to decline to serve gays and lesbians — and, some analysts say, possibly anyone else — on religious grounds. Ms. Brewer should reject the bill, for both practical and principled reasons.

If the bill becomes law, Arizona would likely face another punishing round of boycotts, similar to or worse than those that state leaders invited in 2010 by approving a harsh immigration bill. Several major firms have urged Ms. Brewer to veto the measure. Three state legislators who once supported it have switched sides; opponents, they charge, are twisting the meaning of the bill, but they argue that the policy is no longer worth all the controversy.

Even if there were no threat to Arizona’s economy, though, the governor would be wrong to sign this bill. Some observers claim that it wouldn’t lead to an increase in discrimination, because Arizona has no statewide ban on discrimination against gay men and lesbians to begin with. In fact, there are local ordinances that would be affected. Some legal scholars believe that the measure’s broad language would encourage businesses to refuse all sorts of people, such as unwed mothers. But the impact would be bigger than the bill’s particular words; its mere passage could spur discrimination.

Underlying the policy dispute is the scope and strength of religious protections that business owners bring with them when they open shop in the public arena. We wouldn’t argue that navigating the tension between religious observance and public mandates is easy. We’re not all that sympathetic, but we do understand that some bakers might find it offensive to produce a cake for a same-sex wedding. Conversely, some photographers might not want to accept a job taking pictures at the graduation ceremony of a college that discriminates against gays.

But it strikes us as reasonable to expect that, when you open a store, you will serve any law-abiding, paying customer who walks in the door. Providing service doesn’t mean you approve; it means you’re open for business in a complicated, pluralistic society. To advance a variety of wholly appropriate policy goals, the government must have wide latitude in regulating business, and relevant laws should apply equally in a variety of civil matters — from land ordinances that, say, protect historic buildings to anti-discrimination policies that protect minorities. Special rules that encourage businesses to turn away a long-persecuted minority are particularly unworthy of politicians’ support.

Arizona and other states considering similar measures should go in the opposite direction. Elected leaders should finally pass a policy protecting gays and lesbians from discrimination in the public square. That’s an example the states — and the federal government — would do well to follow.