The testing is not transparent. That's one problem. The other is the technology is always ahead of the testing. Chances are, players are enhancing their performance these days with things other than steroids. HGH, for example. Those magical stem cell treatments Colon, ARod and Kobe Bryant have gotten. There's always a way when there's big money involved.
The other thing that's disturbing is the biggest name abusers--Bonds, Clemens and now Braun--have all gotten off on questionable technicalities.