Regarding T-mobile, they claim that content of the text msg must be legal across all 50 states. Not 100% sure which state and with law causes this but that is the reason they gave me.
the drugs are what is illegal, not the messages.
"No, they clearly acknowledge their service is used for crime - they block these other messages."
For bonus points, find a case where blocking the 'weed' message got someone killed. (You order drugs, the guy says 'weed on the way' but you don't get the message so you don't meet him, he thinks it's a setup and gets mad ...)