Well, who’s gonna pay for your medical care when you inevitably develop drug problems/health issues. So in a socialized healthcare system, you are harming others with it.
(And not offering treatment or making the patient pay for it which they often won’t be able to, would be very inhumane imo)
The law does make sense, if you put it into practice. In practice the dry weight amounts will probably just be checked on the street. Checking your home will require a warrant which isn’t easy to come by, so they’re not gonna bother about cases where it might be three or four plants or this or that many grams.