“The law said “That each and every free able-bodied white male citizen of the respective States, resident therein, who is or shall be of age of eighteen years, and under the age of forty-five years (except as is herein after excepted) shall severally and respectively be enrolled in the militia.””
So, according to the act, only white males are required to enroll in the militia.
That’s the key: the compulsion to buy a gun was contingent on militia membership, which was limited to those who would naturally be expected to contribute to defense of the state which they are a citizen of, AND was matched by active organization and training by the government. Empowered to “call out the militia”, and the militia a subset of the population, the federal government is empowered to direct potential callees (today, anyone registered with Selective Service) to prepare by acquiring minimal equipment. It can all be traced back to an enumerated power.
Health insurance, however, cannot be so traced back to an enumerated power. If it can, then by all means SD can compel residents to buy guns; such is the nature of unlicensed consequences.