Simon Cowell, pictured this month in Beverly Hills, Calif., is leaving his post as a judge on American Idol. (Frazer Harrison/Getty Images)

Tonight marks not only the finale of a lacklustre season of American Idol, but the exit of judge Simon Cowell. Many AI fans have greeted this prospect with glee, seeing it as the departure of TV's number one antagonist. In truth, Cowell is merely moving over to The X Factor (on the same network, Fox). But I don't think American Idol can survive without him.

When the singing competition debuted in 2002, with the British music producer at the helm of its judging panel, TV audiences were taken aback by his tart-tongued candour. Cowell's scathing honesty was unusual for prime-time American audiences, who were used to seeing reality-show hosts mollycoddle contestants. He became not only an American TV star but an archetype: the cranky a-hole. Seeing Simon take down pop-music poseurs every week was one of the main reasons people tuned into American Idol and turned it into a ratings juggernaut.

At times, Cowell has seemed to relish his partypooper status a bit too much -- he knows his role all too well, and actually seems buoyed when the audience greets him with boos. But to simply see him as American Idol's designated naysayer is too easy. For one thing, Cowell has had a well-documented career producing pop music, so his opinion actually carries weight. Secondly, he's been the sole person on the American Idol panel who has been consistently articulate and constructive.

Let's look at his fellow judges. Randy Jackson's vocabulary isn't nearly as estimable as his resume; in RJ's world, you're either "pitchy" or he's "just not feeling it." Former judge Paula Abdul, as we all know, was equally incoherent, but also toothless. Her replacement, Ellen DeGeneres, is slightly more critical, but even less authorititative, given that she's not a musician, merely an enthusiast. Songwriter Kara DioGuardi was brought on two seasons ago to boost the panel's authority. Her suggestions have often been quite insightful, but more than anything else, she seems to be vying for Simon's approval. As for the array of guest judges (Avril Lavigne, Katy Perry, Shania Twain et al.), they're really just the reality-show equivalent of stunt casting -- eye-catching but ineffective.

By parting ways with Simon, American Idol is not only losing its most compelling voice, but its remaining shred of credibility.

YOUR VOICE: Will you watch American Idol after Simon leaves?