On June 26, in McCullen v. Coakley, the U.S. Supreme Court unanimously struck down a Massachusetts law requiring pro-life activists to stay outside a 35-foot “buffer zone” around abortion clinics. Although the outcome of this landmark First Amendment ruling was unanimous, the justices were deeply divided in their legal reasoning.

One key dispute involved an exception in the law: Massachusetts prohibited pro-life protesters, and most other people, from speaking inside the buffer zone. But the state permitted abortion clinic employees within the zone to speak freely. Four of the nine justices believed that this exception doomed the law without any further analysis. The majority disagreed and ruled that a more detailed First Amendment analysis was still necessary.

Residents of Winston-Salem recently became subject to a speech-restrictive law with an exception like the one in McCullen, although the city’s exception is rooted in business cronyism, not political viewpoints. The new ordinance, which took effect July 1, requires door-to-door salesmen in Winston-Salem to obtain a license and city-issued ID before making sales pitches to city residents. The law applies to all forms of commercial sales except one — it exempts newspaper salesmen.

There are, of course, obvious reasons why Winston-Salem’s print newspapers, struggling to maintain their subscriber base in the digital age, would want an exemption from this ordinance and the resulting registration fees. And there are obvious reasons why politicians in the city might want to give preferential treatment to the newspapers that report on them to the public.

But that is little comfort to other salesmen — of, say, encyclopedias, or cable TV, or anything else — who must comply with sales laws from which the newspapers are exempt.

In light of McCullen and other recent cases, this preferential treatment raises serious constitutional concerns. But whether it is constitutional or not, it is certainly bad policy. One of the greatest benefits of free speech is the competition that is created through the open exchange of information and beliefs. Scholars call this the “marketplace of ideas.”

It works like any other free market. Just as competition among businesses benefits consumers, competition among differing viewpoints benefits the public discourse — it helps society separate the strong ideas from the weak ones. And as in any other marketplace, we should be wary of government intervention in the marketplace of ideas.

Supreme Court Justice John Paul Stevens aptly summed up this concern in an opinion years ago: “The First Amendment directs us to be especially skeptical of regulations that seek to keep people in the dark for what the government perceives to be their own good.”

To be fair, favoring the speech of certain salesmen over others may seem far removed from censoring one side or another in an important public debate. But in a robust democracy like ours, there is little risk of our freedoms disappearing overnight. Instead, the greatest threat to our liberty is the slow erosion of our rights, in steps so small that we barely notice.

For this reason, we should be critical of any laws that favor one group of speakers over another — no matter how remote or insignificant that favoritism might appear. Because, if society becomes accustomed to our government playing favorites among speakers, we may soon find politicians and bureaucrats tilting the debate on issues far more important than which salesmen are allowed to knock at our doors.

Richard Dietz is a partner at Kilpatrick Townsend & Stockton LLP. His practice focuses on appeals and constitutional law. He is also a 2014 E.A. Morris Leadership Fellow.