Today is Flag Day, a relatively minor holiday that seems to have fallen off the radar of most Americans, still hot and dazed from Memorial Day and looking ahead to the Fourth of July.

But it’s an important holiday for a number of reasons — not the least of which is that it’s a day (like every other) when legally, people can desecrate the flag.

It was just 25 years ago that the U.S. Supreme Court declared flag burning to be protected political speech.

The United States v. Eichman was decided on June 11, 1990.

“While flag desecration — like virulent ethnic and religious epithets, vulgar repudiations of the draft, and scurrilous caricatures — is deeply offensive to many, the Government may not prohibit the expression of an idea simply because society finds the idea itself offensive or disagreeable,” the Supreme Court held.

Why is this so important?

The freedom of expression is under threat today, from those who would silence speech they find “offensive or disagreeable.” The threat comes from college students who demand “safe spaces” free of any dissenting views, and from radical Islamists who feel that cartoons of their prophet are justification for murder.

In May, two would-be jihadists tried to attack a Garland gathering that featured a Mohammed cartoon contest. They were both killed by police.

There was a disturbing trend of attempts to blame the organizers of the contest.

U.S. News & World Report put it like this: “The Garland attack refocused public attention on the fine line between free speech and hate speech.” And CNN anchor Chris Cuomo claimed on Twitter that “hate speech is excluded from (constitutional) protection.”

But it’s not.

“There is no hate speech exception to the First Amendment,” writes UCLA Law Professor Eugene Volokh in the Washington Post. “Hateful ideas (whatever exactly that might mean) are just as protected under the First Amendment as other ideas. One is as free to condemn Islam — or Muslims, or Jews, or blacks, or whites, or illegal aliens, or native-born citizens — as one is to condemn capitalism or Socialism or Democrats or Republicans.”

That freedom is fundamental to our democracy. It’s too easy to label dissent as “hate speech,” and thereby silence the opposition.

That’s why the Supreme Court was right to uphold flag burning.

A Court that banned flag burning would be fully capable of someday cracking down on the Bible, for example, under the guise of penalizing “hate speech.”

The flag itself stands as a symbol against such nonsense — even if it’s alight.

Flag Day commemorates the day in 1777 when the Continental Congress adopted the Stars and Stripes as the official flag.

The first “Flag Birthday” celebrations were held in 1885 in Wisconsin and in 1889 in New York City. Two years later, the Betsy Ross House held a Flag Day celebration.

But it wasn’t until Aug. 3, 1949 that President Harry Truman declared June 14 as National Flag Day.

In 1966, Congress, wishing to extend the honor, asked the president to declare the week of June 14 as “National Flag Week.”