It wasn't for a long time and it's becoming more of a grey area as more and more states legalize it for recreational use. Talking about illegally obtaining it can land you a ban. Discussion about the politics of it (medicinal, should we legalize it?, the war on drugs, etc.) has generally been accepted for a while now. I had a discussion with some of the ninjas about the topic a couple years ago as it became legal in my state. At the time they still considered talking about obtaining it and smoking it a bannable offense.