The NFL and Marijuana

With the NFL draft coming up in a couple weeks, teams are trying harder than ever to uncover dirt on players. Two players have admitted to using marijuana, Mario Manningham of Michigan and Aqib Talib of Kansas. I don't really understand why using marijuana should affect your draft stock. It's not performance-enhancing. I saw one guy today comparing Manningham to Maurice Clarett- a guy who has committed armed robbery and was pulled over for an illegal u-turn while having in his possession a hatchet, an AK-47, a pistol and 2 other handguns, and an open bottle of Grey Goose vodka. Police had to chase him until he finally pulled over after running over a spike strip and then they had to subdue him, first using their tasers before switching to mace because Clarett was wearing body armor. Ricky Williams has been ostracized from the NFL for years because of marijuana use that is actually legitimized because Williams has high anxiety. Meanwhile you have guys like Leonard Little, who drove drunk and killed someone and has since driven drunk, being allowed to still play. What's wrong with this picture?