A lot of people have pointed out that the evidence in the Mitchell Report would not hold up in court. They point to Roger Clemens in particular. It's as if the Mitchell Report was supposed to produce evidence to be presented to a grand jury or something. If that would have been the purpose, then it would not have been worth releasing.
I think the point was to justify stricter measures to prevent the use of drugs in baseball. Obviously you can only prevent future use, you cannot change the past. If that is the purpose, then I think it does a very good job. It shows that by only getting two people to cooperate, they were able to find evidence against dozens of players. There is no way the public could not come away feeling that drug use is widespread in baseball. It's not just the guys hitting 40+ home runs. It's the starting pitchers, the relief pitchers. It's the low-power, fast running infielders and outfielders, as well as the sluggers and wannabe sluggers. It's the utility bench players. It's the upcoming players and aging veterans. It's future hall-of-famers and guys struggling to get at-bats.
If the public thinks that everyone is using, then it will be hard for the player's union to stop the owners from instituting testing that is on-par with the NFL or maybe even the Olympics. Smart and/or cynical folks will say that players will still find ways to use drugs to get an advantage, but it does not matter. All that matters is that most fans feel like order has been restored. They feel like they are watching a "fair" and "clean" game. The Mitchell Report forces the players' union to accept this kind of testing, or baseball will lose fans, and players' salaries will fall. It's that simple.
Now if three years from now, Alex Rios leads the majors with 25 homers... Well that would be pretty interesting, wouldn't it? I don't think it will be the case. There will the usual fluctuations in hitting vs. pitching, but no amount of drug testing will have much affect on the general proclivity of home runs.