I'm all for them using if they desire, but I also think that they have a responsibility as players to know and abide by the rules. They might as well put their energy into crafting wording in the next CBA that allows the use of it by players in states where it has been legalized.
That would not work. If a guy failed a drug test you wouldn't know where he was when he was using.
It's not just a matter of the legality of the substance. A player could enter the NFL's substance abuse remediation program for alcohol abuse and be suspended if he fails to abstain while under the program's supervision. The wording of the policy seems to suggest they don't test for alcohol as a matter of course, only if there is some other reason for a guy to be put in the program, like a DWI arrest.
The league's concerns are as follows, quoting from the NFL's "Policy and Program on Substances of Abuse" which, by the way, is separate and distinct from the one on performance enhancing drugs:
"Substance abuse can lead to on-the-field injuries, to alienation of the fans, to diminished job performance, and to personal hardship. The deaths of several NFL Players have demonstrated the potentially tragic consequences of substance abuse. NFL Players should not by their conduct suggest that substance abuse is either acceptable or safe."
I don't see the league backtracking on that. Maybe fines and lighter suspensions instead of the heavier suspensions currently applied while keeping the remediation programs in place.
There is one legal issue that most people have forgotten while the converative NFL owners might have it on their minds. Marijuana is still a controlled substance under federal law. Possession, even if medically and legally prescribed under state law, remains a federal offense. It just so happens that law is not enforced. However, banks are loathe to do business with anybody in the "legal" cannabis supply chain for fear they will run afoul of federal money laundering regulations. There's a bill currently stuck in the Senate Banking Committee aimed at easing these banking restrictions. The point being, how "legal" cannabis might be in states where it has been legalized is not yet a settled matter.