Why do some people smoke datura stramonium turned black and has white mold on it, is it still good to smoke?

NO!! Datura stramonium (jimson weed) contains belladonna alkaloids and is very poisonous - especially the seeds (which are what people like to use for hallucinogenic effect.) ingestion of jimson weed can cause acute anticholinergic poisoning and death. Effects include dilated pupils, dry mouth, dry skin, extreme thirst, dry mucous membranes, tachycardia, blurred vision, nausea, vomiting, & coma.
Stramonium. This is a weed grown overseas & carries names like jimson weed, thorn apple, stink weed, devil's cucumber, & others. It is poisonous & can cause hallucinations & delirium. Believe it or not, the greek meaning of it is "mad".