Generally speaking, human beings lie, and data doesn't. Visual evidence, statistical evidence, it was all there. Anyone who thought Mark McGwire did not take performance enhancing drugs was just ignoring the data. Baseball is a very statistically driven game. In no other sport do you get thousands of samples per player (i.e. pitches, which lead to at bats). When you get enough samples, you can make very good statistical predictions on players. A player with a lifetime batting average of .310 will probably hit somewhere between .290 and .320 the next year. More samples, less variance, it's pretty basic.
So when a player undergoes a dramatic shift in his performance based on previous history, something is usually amiss. Injuries cause players to perform worse and those scenarios are very explainable and occur quite frequently. But when a player makes a dramatic shift in the other direction without much to explain it, America's eyebrows become raised with doubt.
McGwire admits in his confession that much of the reason he took steroids was to avoid injury and stay healthy longer. This could very well be true. Baseball certainly isn't football or hockey or any other contact sport, but its regular season lasts 6 months and 162 games. It's not difficult to see how it can become a grind both mentally and physically for a player; and without the aid of performance enhancers, it would be very reasonable to expect minor dings to add up over the course of a season.
Take a look at this page:
With the exception of Roger Maris in 1961, no player who hit more than 30 home runs by the All Star break hit more than 20 in the second half of the year.
Then look at the list. Beginning with Brady Anderson (a guy who hit 50 home runs that year and never more than 24 in any other season in his career), there were 12 instances of a player who hit more than 20 in the second half of the year. Most telling are the 30+ home runs hit in the second half of a season by Mark McGwire, Sammy Sosa and Barry Bonds.
That's data. And I'm sorry, but when you couple that data with each players' changes in physical appearance over the years, performance enhancing drug use just screams out at you. It's my contention that one of the reasons steroids changed the game is that players are more able to maintain their peak performance throughout the year than they would without them. Never mind the additional distance and power the hitters were able to achieve, just look at how they maintained their health for the entirety of the season.
Here is some more minor data to support that, in this case, Alex Rodriquez: http://www.baseball-reference.com/players/r/rodrial01.shtml
From 1996 when he was 20 years old to 2000 when he was 24, he had only 1 season where he played in 160+ games. Beginning in 2001, when he was 25, in 5 of the next 6 years he played in at least 161 games. Not coincidentally, in 2001, he hit over 50 home runs for the first time. By his own admission, those were the years he began using steroids. Play longer at your peak and inflate your numbers. Don't you think you'd be more likely to play a full season when you're 20 or 21 than when you're 29?
The bottom line is that baseball statistics are nearly sacred to American sports fans. If I say 61 or .406, you know exactly what those numbers mean, and who achieved them. So when something taints those numbers and their meaning, it taints the entire sport and its legacy. It's a shame really. Let me ask you this question: if you were offered a guaranteed contract for $114 millions dollars in exchange for taking steroids and negatively impacting your health seven years later, would you do it? Jason Giambi did.
But I'll close out with a little bit of, OK maybe a lot of, cynicism. It's not just baseball folks. It's just about every sport there is if there's enough money involved. Golf might be an exception. It's simply not possible to compete in professional sports without them. If someone's doing it, they're skewing the average and I just don't think that there are any natural athletes able to compete with those who do. So the pressure will always be there to do it. Look for athletes that respond with "I never failed a drug test" as their response. Big deal. Do I suspect Lance Armstrong used them? Yes, I do, but only because of the statistical improbability that he was such an outlier in a sport of probable users for such a long time. Do I suspect Brock Lesnar used them? Yes, I do, but only because of the environment he was in with the WWE and the physique he had back then. It's just not physically possible to carry that much muscle mass and so little body fat with out drugs. Sure, you could be the one in one billion genetic freak that does, but I'm not buying it. He was with the WWE, an organization forever associated with steroid and other drug use. Is Brock clean now, ever since he began his MMA career? He could very well be, and I wouldn't necessarily doubt it. But he's softer now, his physique is more in line with that of a natural athlete than a professional bodybuilder.
I'm just at the point where it's getting tougher to be a fan of any sport, because I'm simply so suspicious about anyone's ability to perform so well for so long. Do I hope the truly outstanding athletes like BJ Penn and George St. Pierre are drug-free? Absolutely. Would I be surprised if they weren't? Sadly, I wouldn't.