A SHOCKING THING HAPPENED last week: I wrote disapprovingly about Oprah Winfrey showcasing hucksters on her daytime show, and nothing happened.Oh sure, an “Oprah” fan asked in an email what I had “brought to this world that is of meaningful contribution to it.” (Answer: I tip generously.) But there was no hate mail. No righteous indignation from the faithful on the order of “Oprah is such a positive force, you’re a terrible person for trying to tear her down.” The response, rather, was mostly positive from those who agreed with the sentiment, nearly all of whom prefaced their remarks by saying, “Good luck with the angry letters you’re going to get” for daring to remark upon the empress’s tattered clothes. The underlying assumption there is that Winfrey is so saintly a figure, so powerful, as to be above or impervious to criticism — an image reinforced by this week’s ABC special “Building a Dream,” focusing on the girls academy she founded in South Africa. While the hour at times felt like nothing so much as a chance to exalt Oprah’s greater glory, the effort is so laudable, such a one-way ticket to heaven, that only a cynic or fool would second-guess it — all the more reason, actually, to flag it when Winfrey lends her authority to dubious enterprises. If that sounds unfair, as John Lennon observed, for messianic figures, it ain’t easy. Widening the lens to view the failings of other mega-stars, however, reveals that when power and influence are attained, that’s precisely when talent needs to be questioned most — with criticism that can be instructive even when it doesn’t feel constructive. TOO OFTEN, MEDIA LUMINARIES are overly shielded even from respectful analysis. They vaguely understand that it exists, but their handlers and entourages deflect anything that might penetrate the bubbles surrounding them, not wanting to tamper with machinery that throws off money the way a sheepdog dries itself after a bath. In this regard, Winfrey is hardly alone. Sifting through the critical invective hurled at NBC’s “The Black Donnellys,” it seems clear that series creators Paul Haggis and Bobby Moresco — fresh off their Oscar win for “Crash” — could have used a sterner hand guiding them. Fox News Channel would also do its biggest noise-maker, Bill O’Reilly, an overdue favor by impressing upon him how off-putting it becomes when he repeatedly whines about being victimized by “smear merchants,” which merely serves to egg on the gadflies that pester him as he stoops to swat at them. Even David Geffen’s much-ballyhooed broadside against Hillary Clinton that so outraged her camp — delivered via Maureen Dowd’s New York Times column — expressed misgivings about the former first lady’s candidacy that she should hear, especially in giving voice to qualms about the prospect of alternating Bush and Clinton dynasties. One recurring lesson is that success tends to erect its own kind of cage. In the case of hit TV shows, that often leaves a program’s architects trapped into choices they might not otherwise make. AT A RECENT TV ACADEMY EVENT, “The Wire” producer David Simon stated as much, noting that his team was afforded such wide creative latitude on the brilliant HBO series because it’s a marginal ratings performer, lowering the stakes. “Being more popular than we were, maybe there would have been forces pressing us that would have made us make decisions that would have been about sustaining the franchise,” he said. “The Wire” will conclude after its upcoming season, as opposed to wrestling with when and how to do so — the dilemma facing ABC’s “Lost.” In knowing the time to say goodbye, Simon told the crowd, “It’s a lot harder when it’s a hit. Because if the whole world is saying, ‘It’s just great, you’ve got to keep going,’ the whole construct of serial storytelling is, ‘Well, I’ll give you more of what you like.’” In short, as intoxicating as it is to be lavished with praise, penthouse views aren’t always conducive to recognizing what’s occurring at ground level. And while there’s never a shortage of acolytes to kiss an A-lister’s golden behind, it frequently requires someone who isn’t on payroll to dare deliver an inconvenient truth.