That, at any rate, is the view of the cattle ranchers of Texas, who claim an off-hand remark Ms Winfrey made during one of her morning shows, vastly popular among housewives, sent the value of beef crashing. Learning about Mad Cow disease, she declared, "just stopped me cold from eating another burger". The next day the price of cattle futures in Chicago fell by 10 per cent.
The ranchers, claiming the second incident was connected to the first, are suing Ms Winfrey under the terms of a Food Defamation Law recently introduced in Texas. According to this law it is possible to libel an orange, a fish, and a piece of meat.
The trial, which got under way last week, is taking place in Amarillo, a town which might be described as the cattle capital of America. One third of the beef consumed in the United States once grazed in the surrounding Texan flatlands.
The people of Amarillo don't seem to harbour any hard feelings towards Oprah. Her decision to move her show, complete with 200-plus production staff, to the dusty, sun-bleached town has been greeted by most of the God-fearing locals as, if not quite the Second Coming, certainly the next best thing.
At the first recording of the show in Amarillo 12 days ago her appearance on stage prompted an ovation from the local studio audience that lasted one and a half minutes. As she arrives in court in the mornings and leaves in the afternoons crowds line the streets, cheering her wildly. "It's really unusual," Ms Winfrey told a horde of attendant reporters. "After all, I'm on trial. And people want to party."
Ms Winfrey was being disingenuous. For the people of Amarillo to have welcomed her so effusively was no less of a surprise than the ecstatic behaviour of the people of La Crosse, Wisconsin, last Wednesday when President Bill Clinton breezed into town. The thoughtlessness of one may have done harm to a local economy; the recklessness of the other may have done harm to the entire country. But America is a place where all judgement, all reason, all prejudice, even, is suspended when a celebrity looms into view.
Racially torn as Mr Clinton proclaims America to be, the fact of Ms Winfrey's black skin has not prevented her from ascending the Mount Olympus of the television age. According to Fortune magazine, she is the highest paid entertainer in the world, with personal assets worth $414m (pounds 245m).
But she is far more than an entertainer. By addressing herself five days a week to the domestic, economic, amorous, dietary issues that affect ordinary people - especially women - she has become America's counsellor- cum-psychotherapist in chief.
As for her power, it is impossible to quantify, save to note that the books, records, physical fitness programmes she recommends on her show have a habit of recording an instant quantum leap in sales.
The logic of the Texan ranchers' law suit is that, on account of the very same herd mentality, the commodities she criticises on her show are susceptible to a no less dramatic slump.
Ms Winfrey has not testified yet. But what she has heard in court has been the ranchers' lawyers claiming that there's "not a snowball's chance in hell" of BSE catching on in the US and that, accordingly, remarks which throw doubt on the safety of America's favourite dish could be described as defamatory.
The defence is arguing that the ranchers' suit is null and void because it rests on the contention that Ms Winfrey is obliged to suspend her constitutional right to free speech. "Are you not trying to silence the most powerful voice in America?" one of Ms Winfrey's attorneys asked a witness for the ranchers.
Public opinion in Amarillo and beyond is on Ms Winfrey's side. Bumper stickers proclaiming "Amarillo loves Oprah" were doing a roaring trade last week. Another bumper sticker declared, "the Only Mad Cow in America is Oprah". But few were buying it. In part because Winfrey is so popular but also, perhaps, in part because, in the light of developments in Washington, not even the ranchers believe it any more.