The opiodergic system doesn't describe behaviour any more than gravity does. Stimulating the opiodergic system provokes a wish to repeat the activity. Gravity provokes a need to put a roof over our heads to protect from stuff falling, to put things down rather than up. That's not describing behaviour, that's describing conditions for behaviour. Auferre, trucidare, rapere, falsis nominibus imperium; atque, ubi solitudinem faciunt, pacem appellant.
