Mike Huckabee, the Family Research Council and others have declared this Chick-fil-A Appreciation Day. And while Americans should head to the chicken-sandwich restaurant to show their support, they should also take the opportunity to reflect on the intolerant left.

Watching liberals react to Dan Cathy’s comments on marriage and family over the past two weeks revealed their real agenda: shut down and silence anyone who doesn’t agree with them.

Big-city mayors from Boston, Chicago, San Francisco and Washington, D.C., vowed to use their political clout to keep Chick-fil-A out of their cities. When the company’s top spokesman died unexpectedly last week, one liberal friend of mine declared on Facebook, “Oh, karma, you crafty bitch.”

I thought liberals were the ones preaching tolerance?

The Chick-fil-A kerfuffle helped clarify a point conservatives have been making for years. Liberals are interested in debate only when they’re winning. And on the issue of marriage, they’re 0-for-32 in states that have put the question to voters.

That offers some explanation why mayors Tom Menino, Rahm Emanuel, Ed Lee and Vincent Gray promised to punish Cathy because of his differing view on marriage. What’s scary, though, is that individuals with this much clout think it’s appropriate to use that power to exact the punishment.

Never mind that Chick-fil-A takes no position on homosexual marriage, a point the company reiterated during the media firestorm. It didn’t matter. Liberal journalists fanned the flames by deeming Cathy’s comments endorsing the “biblical definition of the family unit” as anti-gay.

And to make matters worse for the mayors, Chick-fil-A hires employees and serves customers without regard to their sexual orientation. So in this case, the only people discriminating are the mayors.

Sadly, this is a trend that’s played out too frequently of late.

Liberals used the same tactics they’re now employing against Chick-fil-A earlier this summer to attack University of Texas professor Mark Regnerus. He published one of the most comprehensive studies examining the outcomes for adult children whose parents had same-sex relationships. Rather than learn from Regnerus’ study or debate its findings, activists instead have sought to destroy his credibility and banish him from public discourse.

There’s even an ongoing inquiry to examine his work. Anyone can request such a probe of the University of Texas. In this case, it came from provocateur Scott Rosensweig, who uses the pseudonym Scott Rose. He claims “scientific and scholarly misconduct” on the part of Regnerus and has made it a top priority to discredit and silence the professor.

Rosensweig isn’t alone. A group of 200 scholars wrote a letter to the editor of Social Science Research, where the Regnerus study was published, questioning how the journal could print such a thing. The publication’s own audit, released last week, “did not find that the journal’s normal procedures had been disregarded, or that the Regnerus paper had been inappropriately expedited to publication, as some critics have charged.”

The whole affair illustrates, once again, the left’s intolerance of opposing views on hot-button issues. Regnerus could have reached a different conclusion and avoided the backlash. But because his results conflicted with the left’s preferred narrative on same-sex parenting, the critics pounced.

Peter Wood wrote in the Chronicle of Higher Education:

We get it: Researchers take note. Publish only findings that support the gay agenda. Departures from that rule will be punished up to and including career-ending academic show trials.

The summer wouldn’t be complete without an attack on the Boy Scouts of America as well. Earlier this month, after a two-year review, the organization reaffirmed its longstanding position of refusing membership for openly homosexual individuals.

That’s within its constitutional right as a private organization, but it was unacceptable to a group of individuals who would rather impose their own beliefs and trample on the Boy Scouts’ rights. The Human Rights Campaign and Gay & Lesbian Alliance Against Defamation immediately condemned the organization, calling it a “discriminatory policy” and “dangerous message.”

Americans have spent more than 200 years debating and disagreeing on a range of contentious issues. That’s why we treasure free speech. But these recent actions — using political threats against a restaurant chain, advocating for the termination of a university professor and attacking a private organization’s right of association — threaten to undermine that very right.

Rob Bluey directs the Center for Media and Public Policy, an investigative journalism operation at The Heritage Foundation. Follow him on Twitter: @RobertBluey