Don't get me wrong, I'm not denying that the notion of juicer opera stars has a certain ring to it (Villazon and Alagna hosting notorious cortisone parties in the Covent Garden dressing room...nefarious agents who take you aside and ask if you would really do "anything" for that b-flat...Ben Heppner as the cautionary tale every rookie must learn) but I think the sports analogy is off the mark. The problem with steroids in sports is that it actually changes the nature of the enterprise to the point where the drugs are part and parcel of what people consider the state of the art in the field. And it's uncomfortable to know that you're rooting for something which may be essentially artificial.
But the issue here for opera has little to do with the thing itself. It's a simple case of opera stars getting roped into the same demands that rock stars and other international performers have been facing for years. Unfortunately for them, while its considered OK and even kind of endearing for Keith Richards to go onstage strung out and phone in a set from time to time, no one has much sympathy for an opera singer on an off night.
So definitely a big problem, but let's be clear that the appropriate reference is more Stevie Nicks: Behind the Music than Juiced: The Jose Canseco Story.