Medical marijuana is legal in 33 of the 50 states and all of that has only happened in the last few years. The fact that that most of if not all of these players were breaking the law before that time or in states where it isn't legal seems to be the point you are missing. Marijuana is not the only way to treat stress, depression, or other mental health issues. People self prescribing is definitely not the answer. Plus, playing in the NFL is a privilege and these guys know the rules before signing up.
On top of all of that, Josh Gordon's use of marijuana, alcohol, and cocaine clearly never helped his mental health. He is an all world talent but he is a tormented individual who needs help that those drugs don't bring. Let's be real for a minute, he is stepping away because he is about to be suspended for illegally using drugs.