Let them all disagree, they'd all be wrong.
'cuz they would be better if they didn't smoke weed. Especially as they get older.
Sponsors want as much revenue as they can get. They know that hipsters who cherish getting stoned as one of their priorities in life spend their money really easily on stupid things. Sponsors probably encourage it.
I think the fact that many of the side effects of marijuana not only could be very very dangerous on a football field but also the fact that if a player suffered a severe reaction during a football game it would be very very bad publicity, dangerous to the player, and dangerous to anyone around him or in the stadium potentially. I understand that psychotic episodes are rare but to have someone suffer from one on the field because they were to smoke before a game or to lessen their pain would be a horrible PR problem for the league and also endanger the lives of the NFLs employees. The public opinion around weed is certainly softening so I wouldn't be surprised for the rules to change especially by the next collective bargaining but I think the NFL has a legit reason to want make sure its employees are of sound mind when they are playing on Sunday.