Disclosure won't allow baseball to start with a clean slate. Disclosure of the other 103 will still leave out a hefty number of individuals who either flew under the radar despite being users or who just happened to cycle off before their test, or guys who simply weren't part of the random selection process (I'm assuming they didn't "survey" EVERY player).
You also can't have a clean slate when even now there are players using PEDs...the players and their handlers are getting smarter, there are labs creating new designer steroids, and there is stuff out there that is not on MLB's banned substance list.
Frankly I am not at all appalled at ARod's alleged usage. Put yourself in ARod's shoes:
Here you are, one of the most naturally gifted players the game has seen, multi-tool player, in a league that increasingly loves the long ball (I'll focus a lot on HRs, just to make a point):
In 1991, only 2 players hit 40 HRs, only 12 hit over 30.
In 1992, 2 hit over 40 and only 10 reached 30.
In 1993, while you are in the minors, in MLB 5 reached 40 HRs, a total of 22 hit 30+...and that list includes such "powers" as Ron Gant, Phil Plantier, Dean Palmer, Mickey Tettleton, R. Wilkins..and there are hints that some of these guys are using steroids.
In 1994, you're still in the minors during this strike shortened season where no one played more than 116 games...25 players were on pace to reach 30+ Hrs, many of them being those rumored to be using PEDs.
In 1995 you're almost ready to break in to the league, and here you are, KNOWING that your 10x better than many of MLB's sluggers...you see Albert f***ing Belle slug .690 with 50 HRs, the first 50 HR season in some time, Dante Bichette hits 40, Buhner hits 40, Palmeiro hits 39, 21 guys end up with 30+, christ even John Valentin hits 27, and you hear more whispers of 'roid use.
So you break in in 1996, want to make a splash, you've got an ego to start with, maybe you choose to use right away...or maybe your 36 Hrs as a rookie are legit...who knows. What you DO know is that your 36 HRs puts you around 23rd in MLB...23rd! f*** that, I'm not going to be outperformed by guys that can't hold my jock, guys like Ellis Burks, Todd Hundley, Caminiti, Vinnie Castilla, Dean Palmer, Jorge Berroa. Now you're in the bigs and you KNOW what these guys are doing to reach the heights they're reaching...so you consider doing it too.
In 1997, still knowing you have more talent than most, you only hit 23 Hrs, .300 Avg, 84 RBI's and you're not about to watch Nomar, or Raul Mondesi, or Chili Fkn Davis, Eric Karros, Matt Williams, Tony Clark, Burks, etc. outhit you. You're gonna get yours.
1998 you hit 42, 12th in MLB
1999 you hit 42
2000 you hit 41, but that isn't enoough...so you turn up the juice.
2001 you hit 52, and you're out-homered by Luis Gonzalez? f*** that!
2002 you hit 57
From 2003 to 2008 you go 47, 36, 59, 35, 54, 35.
You've got yours and you know that there are only 3 definites in life...death, taxes and steroids work really well.
While I'm speculating, it is not hard to imagine this playing out this way for ARod and for many other MLB players. Now, where exactly he started using? We can speculate on that, but I'm pretty sure it was before being caught in 2003.
Steroid and PED use in baseball is epidemic and contagious. There's a lot of ego involved and the financial rewards are too huge to forego. I understand why these guys do what they do and since they're not my role models, heroes or friends I don't really give a f***.