If you won't punish one star for using drugs, then why punish the other?

Tim Lincecum got rung up for speeding on I-5 near Vancouver, WA and got caught with pot in his car, a charge that has since legally been settled. As for whether the Giants ought to punish him... if they're not going to punish their biggest star ever for using performance enhancing drugs, then why should they punish their star pitcher for smoking a bowl in the car en route to WA?