So if the Supreme Court rules that it is unconstitutional to force a person to do (or not do) something (like buy health insurance) does that mean the Feds can't legally stop me growing marijuana in the back yard?
As I see it, one can do whatever one likes but with the risk of losing privileges. Such as driving on state & federal roads (in the case of public drunkenness) or a fine for breaking the speed limit. In cases of extreme crimes, losing freedom. But I presume that is because of potential interactions with others--drunk driving is harmful to others, speeding is more dangerous . . . society trying to govern interactions through its laws.
So as I understand it, the distinction in your post may be in whether the government can force interactions apart from the privileges it already offers (education, public buildings, etc). PRIVATE insurance companies are inherently not a privilege provided by the government.
I might be fine if you were to grow marijuana in your backyard if it didn't impact others. (And I'm not sure it would.) But I could still be upset if the government, say, made an appointment for me to see someone without my consent or court order. And that is far less than requiring payment from me from something neither a tax nor self-chosen.