Nothing about bodybuilding is natural.
Lifting weights and useing machines to develop your muscles is not natural. Ingesting high amts of protein isolates via protein powders is unnatural. Taking superphysiological amounts of any nutrient such as creatine, arginine/citrulline, l-carnitine, bcaas, etc. is unnatural. High potentcy herbal extracts such as tribulus are unnatural, fat-burners (no explanation necessary).
In other words - everything about bb is totally unnatural: the training, the supplements, EVERYTHING. Some supplements are illegal some are not (it depends on what country you are in). No one who bodybuilds is engaging in a "natural" activity.
BTW, Croatch - don't forget - that one cycle permanently altered your body on a genetic level. Have a nice day.