Celebrities be allowed to publicly discuss smoking marijuana, or anything else, without legal consequences if the state doesn't allow recreational smoking. We have a Constitution that guarantees us a right to free speech. That right includes speaking about even unpopular or uncomfortable topics. Under no circumstances should this kind of speech be curtailed.
Okay, so you still wouldn't want to shout "fire" in a crowded movie theater. It might not be a good idea to talk openly about marijuana use. But just because someone talks about it doesn't give law enforcement enough reasonable evidence to make an arrest. If an actor makes a blanket statement that they smoke, it's not enough. Hopefully, most people wouldn't go on TV and say "Hey, I have 5 kilos stashed in the room back at my place."
Celebrities have a wide public reach and a huge influence on the masses. Publicly discussing smoking marijuana in a state that doesn't allow recreational smoking sends mixed messages about the state laws to their followers. By discussing an activity that is against the law without being legally reprimanded for the activity, others may feel that it isn't important to follow the law, and that if caught engaging in such an activity will not result in serious consequences. Celebrities should be aware of the example they are setting for their followers.
Celebrities should follow the state law. If a state does not allow recreational smoking then the people of the state, through their elected representatives, have reached that decision. Celebrities should not be allowed to break a law just because they disagree with it. That sets a dangerous precedent. Celebrities are people just like the rest of us and they should follow the law.