Second, addiction suggests lack of full consent.
And clearly there are negative externalities to such a choice. That person may have a family, other debts they don't pay, may make poorer life choices as a result of blowing their paycheck , may choose violence or drugs or self-harm ... most of which will cost taxpayers and other third parties.
Also "enjoy" is a loaded term.
Also, just as likely this person is already abusing their body with drugs.
This planet is HARD and not every thing born on it is going to have a good time. Ask the squirrels my neighbors shoot at if life is fair.
A more accurate devils advocate could be one who suggest that forms of manipulation and coercion should be allowed because its physically possible in reality to do so.
As for when coercion is used... I don't think it's useful to play devils advocate for coercion. That one is settled, everyone already agrees that coercion is bad.