To paraphrase a popular TV commercial, free speech is “priceless.”

As protesters and delegates gather for this year’s national political conventions - Democrats in Denver starting Aug. 25, Republicans in St. Paul Sept. 1 - that’s a constitutional principle well worth noting.

The conventions and their host cities are bracing for thousands of demonstrators. For Democrats, one group plans actions “commemorating” the violence-filled 1968 Democratic National Convention in Chicago. The GOP will see protests from groups including the anti-war “Code Pink” and Veterans for Peace, as well as individuals speaking out on myriad other issues that will remain after the Bush administration.

The First Amendment requires that police and public officials have more supportable reasons to shut down protests than vague concerns over order, safety or national image. They certainly can’t legally stop the messengers just because they don’t like the message.

It’s also worth noting that there can be a hefty price to pay for running roughshod over free speech. New York City, just the other day, provided the latest example of that combined constitutional and fiscal lesson.

News reports said the city agreed Aug. 19 to pay $2 million to settle claims by 52 people arrested in April 2003 in a street protest against the then-recent U.S. invasion of Iraq. A New York Times column reported the city also spent an estimated additional $1 million in preparing a legal defense it no longer needs.

The Big Apple protesters were charged with blocking pedestrian traffic - a common charge when police break up public demonstrations. Though city officials made no admission about the validity of the charges, a Times account said videotapes showed the protest didn’t disrupt the public except perhaps where it “slowed a few people carrying coffee into work.” On the original charges, just two people went to trial: Both were acquitted, and charges against the other 50 were dismissed.

The lesson isn’t limited to Gotham. In 2007, Seattle’s insurance company agreed to pay $1 million to settle damages owed 175 people wrongly arrested in 1999 for being in a “no-protest zone” during a peaceful demonstration against the World Trade Organization. A jury already had held the city liable for the improper arrests. The payout followed an earlier $800,000 settlement stemming from the same WTO meeting.

The District of Columbia paid out millions to settle claims stemming from arrests in 2002 during protests against the World Bank and International Monetary Fund. And after the last Republican national convention, in New York, the city settled for more than $230,000 with 108 people out of nearly 1,800 people charged with disorderly conduct or obstructing justice. Officials said more than 90 percent of the charges were dismissed without trial.

In each example, the government shut down protests “now” and dealt with damages - to taxpayers and constitutional rights - “later.” Even on a practical level, it’s not fair that taxpayers must fork over hard-earned money to fund settlements paid out for preventing others from speaking out. More important, that’s not how free speech and democracy work.

Well-expressed or wacky. Irritating or illuminating. Respectful or raucous. There’s nothing in the 45 words of the First Amendment that sets out any such qualifications or limits on protests. Time and again in our history, from women’s suffrage to civil rights to tax protests, to name just some, voices first raised in the streets - to the disgust or disappointment of some - have led to significant, positive changes in law and American life.

Yes, local, state and federal officials can maintain public safety, protect the rights of others and guard against kooks and terrorists who would do this nation harm. But the “order” in law-and-order doesn’t mean a mandate to enforce a government sense of orderliness.

Convention planners, intent on scoring political points with a well-run show, and city officials aiming to present a positive urban image, might prefer otherwise. But Americans have a right to express themselves in ways that ensure that public officials, and even would-be presidents, will see their signs and hear their voices.

The citizens of Denver and St. Paul, and Americans everywhere, should hope officials in those cities already have considered both the constitutional and monetary costs of silencing voices that have a right to be heard.