More than half a century ago, the great media critic AJ Liebling memorably described the first amendment's outer boundaries. "Freedom of the press," he wrote, "is guaranteed only to those who own one."

It's an elemental truth you can be sure Glenn Beck is pondering these days. Beck's highly rated programme on Fox News, and indeed his career, hang in the balance because of his recent comments that Barack Obama is a racist with "a deep-seated hatred for white people".

Not that Beck's incendiary remarks hurt him with his audience – which, one imagines, comprises mostly unemployed white men with nothing better to do when his show comes on at 5pm than to sit in front of the TV set while polishing their guns.

The problem, rather, is that an increasing number of advertisers – 36 at last count – don't want to be associated with Beck's show. And that's got to have Rupert Murdoch, the owner of Beck's press, wondering whether his newest star is worth the hassle.

Beck's grotesque description of Obama is hardly out of character. We've all seen the YouTube video of Beck talking about the president against a backdrop of goose-stepping Nazis. Earlier this year, in a too-nice New York Times profile, those of us who are not regular viewers (that is, just about everyone who is reading this commentary) learned Beck was passing along rumours that Obama was building concentration camps. Then, too, the liberal watchdog group Media Matters for America has been documenting Beck's outrages for years, going back to his days of denying global warming on CNN Headline News.

What is different this time? A concerted effort by an African-American social-action organisation called ColorofChange.org to pressure advertisers into pulling out. By early this week, executives of such powerful corporations as Wal-Mart, Lowe's, AT&T and Verizon Wireless had announced they no longer wanted to be associated with Beck's dangerous rhetoric.

As much as many liberals detest Beck and other rightwing cranks (the closest analogue is CNN's Lou Dobbs, a giver of aid and comfort to the so-called birthers, who question Obama's national origin), they are reflexively squeamish over the notion of anyone trying to interfere with freedom of speech. Indeed, when Bob Garfield, co-host of National Public Radio's On the Media, interviewed ColorofChange.org executive director James Rucker a few days ago, Beck's right to speak was Garfield's principal line of inquiry.

But Beck's freedom to say what he wants would be threatened only if the government were trying to censor him. Beck's first amendment rights can hardly be violated simply because James Rucker is exercising his own first amendment rights. And if the measure of one's freedom of expression is being the highly paid host of a national cable news programme, well, damn it, I demand my rights, too.

In the American media system, commerce is a rough substitute for conscience. You may recall that, in 2007, Don Imus lost his nationally syndicated radio show when advertisers pulled out over Imus's description of black members of the women's basketball team at Rutgers University as "nappy-headed hos". (Not that it was much of a come-uppance. Within months another network came along and put him back on the air.)

We live in a moment when gun-toting extremists show up at anti-Obama rallies to denounce the president as a socialist Nazi who wants to set up death panels modelled after Hitler's campaign to eliminate disabled people. Emotions are running high – higher than they might were Beck not spreading his hateful lies. If Fox News were a responsible news operation, it would have taken Beck off the air months ago.

If Wal-Mart and Lowe's can do what Rupert Murdoch and Roger Ailes won't, then good for them. Let Glenn Beck exercise his first amendment rights like most of his ilk do – on a street corner somewhere, ranting to strangers, hoping a few passersby might toss a dollar or two into the empty coffee can at his feet.