A professor friend pointed out something canary-in-the-coal-mine-ish out to me yesterday. He said that the fact that a number of big-city mayors — New York’s Michael Bloomberg a notable, and honorable, exception — are now on the record saying that a business whose owner believes what half the country believes about marriage is unwelcome to trade in their city is a startling and alarming thing.

Of course these mayors would get their butts sued off if they tried to use the powers of government to impede Chick-fil-A from engaging in commerce there. Still, the idea that they would even think of such a thing, and indeed take pride in saying so publicly, is shocking.

G. Jeffrey MacDonald calls this a “Ground Zero mosque” moment for the left. Excerpt:

Unfolding is a progressive parallel to the “Ground Zero Mosque” controversy that riled up conservatives in 2010. When the Park51 mosque was proposed, conservatives debated whether a Muslim center near the site of the Sept. 11 attacks would inherently disrespect the site by its sheer presence. For mosque opponents, the World Trade Center site is hallowed ground and would be tainted if certain religious ideas were to garner institutionalized expression nearby.

Now it’s progressives’ turn to exercise the same principle, even though they vehemently opposed its usage in the Park51 case. The idea holds that certain places, which are de facto “sacred” by their associations with bigger-than-life events, would be corrupted if an unpopular religious viewpoint were granted a symbolic presence there. Chick-fil-A is such a symbol, as was Park51. Zealots of all stripes will have none of it.

What’s different this time is how mayors have embraced what was previously regarded as a dangerous stance. In 2010, New York CityMayor Michael Bloomberg brushed aside conservative angst and sided with Park51 on the grounds that barring unpopular religious expression would violate a core American value. On July 27, Bloomberg called his fellow mayors “wrong” for trying to block Chick-fil-A.

Now progressive mayors are showing none of Bloomberg’s confidence in that American value or in freedom of expression. They are instead insisting that unpopular religious views must be kept out, lest what is sacred in their cities – namely the cause of gay rights and same-sex marriage – be threatened or defiled by detractors.

What the progressives are doing is actually worse, for a couple of reasons. One, Park 51 opponents didn’t say that all mosques are unwelcome in the city; they only said that putting one so close to where mass murder took place in the name of Islam is offensive. And unless I remember something wrongly, they didn’t propose, as some of these mayors have done, to use the levers of city government to prevent the mosque from being constructed. As someone who agreed that the mosque plan was insensitive and ill-advised, I strongly would have opposed the government getting involved to tell the mosque-builders they ought not do this. If NYC Mayor Bloomberg had tweeted about the Park 51 mosque that he “strongly recommend[s]” that the mosque builders not set foot in NYC, there would have been an outrage — and a completely justified outrage, too.

But when it happens to Christian businessmen who hold a view unpopular with urban progressives? Crickets.

Anyway, MacDonald points out that if these progressive mayors object to the presence in their cities of people who hold traditional views on same-sex marriage, then they had better be aware of who exactly they’re demonizing. More:

This principled position sends a not-so-subtle signal to America’s largest and fastest growing faith groups, which overwhelmingly oppose gay marriage: you’re not welcome here, either. That’s bad news not only for religious freedom, but also for legions of new immigrants, single mothers and homeless people who depend on religious outreach to help them meet basic needs.

The Roman Catholic Church, for instance, opposes gay marriage. It also operates Catholic Charities, the largest private social service provider in the country. As a matter of faith, Catholics aim to grow their ranks, help more people in need and add new parishes over time. They strive to grow their enterprises in big cities. But as Chick-fil-A found out, mayors will fight efforts as mundane as selling chicken if people at the helm also oppose gay marriage. Why should Catholics or Catholic Charities not be targeted on the same basis?

Others would be impacted, too. America’s fastest-growing faith groups, including Assemblies of God, non-denominational evangelicals and Mormons, by and large do not support same-sex marriage. If the principle used against Chick-fil-A is applied consistently, these groups – as well as all but the most liberal of synagogues and mosques – will face uphill battles to get permits to open houses of worship, shelters or soup kitchens in big cities.

I doubt that city officials at this point would seek to apply this principle consistently. After all, Chick-fil-A is a chain they may not use, and it’s owned by white Southern evangelicals, who are easy for them to hate. But I have every expectation that mayors and city councils in the near term are going to use non-discrimination laws to make it very hard for these religious groups to do anything more in the cities than meet to pray and worship.

Canary in the coal mine? I think so.