The controversy over comedian Ben Stiller’s latest movie, “Tropic Thunder,” is only partly about the words and the theme that appear in it.

The ‘R’ word (for “retard,” which reportedly is heard more than 15 times in the film) is as offensive as the ‘N’ word, say those who advocate on behalf of people with developmental disabilities. Thus, the film opened this week to protests in Spokane and many other American cities where demonstrators asked moviegoers to stay away.

What is at issue more than the insensitive use of a painful word, however, is a longstanding willingness of many people to find humor at the expense of the disadvantaged. The victims are largely voiceless, so those who rally to their defense often urge remedies that include not only box-office boycotts but also bans on the use of certain words.

That’s understandable.

But freedom of expression has survived as a bedrock American value for 217 years because we’ve had the courage to uphold it not just when it was easy, but also in defense of unpopular speech. The individuals and organizations that are upset by “Tropic Thunder,” to their credit, are countering what they consider an offensive portrayal by using their own First Amendment rights.

By loudly encouraging theater patrons to save their money, of course, the protesters risk generating more interest in the film than they quell. But they are also raising public consciousness while appealing to human decency. Some would-be patrons may well reconsider, but even many who see the movie anyway are likely to acquire a different understanding than they would have without the debate.

That kind of understanding was desperately needed by the reviewer who wrote for E! Online: “Some viewers might find something offensive if they were able to stop cackling long enough.”

As you’d expect, star and director Stiller says he wasn’t trying to offend anyone, but, hey, it’s satire and that happens.

What the protesters recognize as well as he does is that pop culture’s influence extends beyond the venue. T-shirts bearing the script line “Never go full retard” already are on the market and parents of intellectually disabled children know the dialogue will be mimicked in classrooms and corridors.

For years, the phrase “mentally retarded” was accepted as a replacement for earlier clinical terms that had acquired slur-like qualities. It’s not really any one word that’s the problem, it’s the attitude.

That’s why, tempting as it is to follow their legitimate box-office protest with a censorship drive, those who object to the tastelessness of “Tropic Thunder” should keep fighting free speech with more free speech, not with a gag.