You could probably spend a lifetime reading the academic literature about the practical consequences of the minimum wage for employment. Despite reams of hard data, economists still squabble over the question. (Keep that in mind when you hear rosy projections about new programs. If economists can't agree on how a program has worked in the past, then how much weight should we give predictions about how one will work in the future?)

But you don't see many moral arguments over the minimum wage, except for vague assertions that it's wrong to pay people less than a certain amount. The moral case against a minimum wage is scarcer still, so scarce you might think there isn't one. But there is, and many people find it intuitively appealing.

Just look at the debate over gay marriage.

Gay marriage has soared to new heights of acceptance; 60 percent of Americans now find it unobjectionable. There are lots of reasons for this, but as a political matter the change has been driven by two basic arguments. The first is an egalitarian syllogism: (a) straight people have a right to marry, (b) people have equal rights, so (c) gay people have a right to marry.

That argument rests on an even more basic one, grounded in liberty. As the Supreme Court majority put it in Obergefell: "The right to marry is a fundamental right inherent in the liberty of the person. . . The Constitution promises liberty to all within its reach, a liberty that includes certain specific rights" — rights such as choosing your marital partner. A majority of citizens cannot deny that liberty to a minority simply because they disapprove.

A slogan from the gay-marriage debate put it a lot more succinctly: "When do I get to vote on YOUR marriage?"

This neatly captures the sense that when two grown men or women consent to something, a third party has no business butting in to overrule their arrangement. Just because a majority of voters in a city or state find the arrangement morally objectionable does not mean they should be able to nullify it by a show of hands.

Oddly, this view — entirely correct, by the way — prevails most in liberal bastions that lately have been enthusiastically ignoring it. Just a few days ago Washington, D.C., approved a voter initiative that would hike the minimum wage to $15 an hour. The same day, a New York panel appointed by Gov. Andrew Cuomo (D) recommended an equivalent wage for fast-food workers; the state's labor commissioner could impose it by fiat. The city council of Portland, Maine, has approved a $15-wage referendum for November. But more conservative places have raised the legal wage floor as well. Last November, voters in Alaska, Arkansas, Nebraska, and South Dakota approved minimum wage hikes in their states.

The parallel should be plain. When Adam and Steve freely consent to a relationship — whether it amounts to a fleeting sexual encounter or a loving partnership lasting unto death — then it's nobody else's business if they do. So why should it become a matter of public deliberation simply because money changes hands? If Adam offers to pay Steve $3 an hour to flip burgers at his fast-food restaurant, and Steve agrees, then what right does anyone else have to veto their agreement? To borrow a line from the late political philosopher Robert Nozick, why should the state interfere in "capitalist acts between consenting adults"?

All analogies are inexact, and this one invites some obvious objections. You might say, for instance, that intimate relations fall into a different category than economic ones. The former are profoundly personal, while the latter are impersonal to the point of being mercenary. So the state can regulate the latter but not the former.

The trouble with that objection is that it establishes a moral hierarchy for personal relationships, deeming some more inherently valuable than others — which is precisely what opponents of gay marriage want to do. They claim straight relationships are inherently more worthy of state recognition than gay and lesbian relationships. Do progressives really want to accept that line of reasoning?

Other objections to the analogy suffer from the same problem. You could say allowing Adam to pay Steve only $3 an hour is immoral, but outlawing relationships that some people consider immoral was the whole point of gay-marriage bans. You could say allowing Steve to work for $3 an hour will affect other workers who'd rather not, so government should forbid him to for the sake of society at large. But allowing government to forbid consensual activity that "affects society" amounts to a regulatory license of infinite scope: With a little creative thinking, anything can be said to affect society.

True, at present all of this seems thoroughly academic. The likelihood that the U.S. will abandon minimum-wage laws anytime soon sounds almost preposterous. Then again, once upon a time so did the idea of gay marriage.

The article originally appeared at The Richmond Times-Dispatch.