It is illegal for consumption. Dried/Powdered cactus possibly could be interperated as prepared for ingestion, so you could possibly be arrested, but i doubt it would hold up in court, unless they can prove beyond a reasonable doubt you were going to ingest it.
If you are unfortunate enough to find yourself in a situation in which a cop is holding up a baggie of powdered incense, asking you what it is, just say its spirulina, a blue-green algae. Its a health food supplement. If he knows what it is already somehow, act dumb. "What?? It contains a schedule 1 substance??" "I was just going to use it for ______________."
Be careful. Dont go around telling everyone. Its a beautiful, unbelievably healing plant, use it respectfully and responsibly.