After deciding the Obamacare is not a tax and therefor not constitutional through Congress's authority to tax, the only justification for the individual mandate is the Commerce Clause. This gives Congress the right to regulate interstate commerce.
Congress has used torturous reasoning to stretch their authority. At one point they declared schools to be weapons free zones. Their reasoning was that weapons in schools discouraged learning which led to a less educated populous which could affect interstate commerce. The Court did not buy this argument.
In the case of Obamacare, the argument is that not participating in commerce affects it. While this is true, it is a troubling expansion of Congress's power.
In the 16th century wool began becoming important to the English economy. In order to promote the wool trade, several laws were passed. Clothing had to be made from wool. Even burial shrouds had to be wool. Things went a step further in London where the knitters guild got a law passed requiring every resident to own a flat wool cap.
If Obamacare's individual mandate is allowed to stand then there is nothing stopping Congress from passing this same type of legislation.
This is where the disconnect lies between liberal and conservative. Liberals have no problem with an all-powerful government. They see the government as the solution to all problems. Conservatives want a government with well-defined limits and distrust centralized planning.
Obamacare itself is an argument against an expansive government. No one in their right mind would call it a great piece of legislation. It is a series of compromises and bargains balancing the most that some Democrats would accept against the least that other Democrats would accept. The Republicans were not even part of the negotiations.
Four of the justices seem untroubled by expanding governmental authority. Not surprisingly, these four were appointed by Presidents Clinton and Obama. They see the Constitution as an out of date document. Like President Obama, they would prefer a much longer document that spells out positive rights. If they were to draw up a new constitution then this case would never have come to court because their new document would have embedded a clause for mandatory health care.
The other five see the dangers. No matter how tempting it may be to let this case through it sets the precedent for laws that are less desirable.
The government would have been on more solid ground if the law had somehow managed to differentiate itself so that a clear line could be drawn between this and future laws. The government's attorney tried to argue that this is a unique case because health care affects everyone. Justice Kennedy (the most likely swing voter) pointed out that most people will need health care in their life but everyone will die and be buried. What would stop the government from requiring burial insurance?
No matter what you think about Obamacare itself, the larger issue is the continuance or abandonment of limited government. If Obamacare passes the court then we might find ourselves wearing wool caps.