So the Patient Protection and Affordable Care Act (Obamacare) is constitutional, according to the Supreme Court. Does it actually conform to the United States Constitution? And does that question actually matter to anarchists? I'd argue "no" on the first question, but I think the latter is a more important question if we are to be effective in building institutions and relationships that serve our interests and crowd out the state's monopoly on legitimacy.
As anarchists, we find ourselves in an environment run by statists who attempt to get away with all manner of illegitimate actions and policies. For us, those acts and policies are not illegitimate because they are inconsistent with the state's own internal rules. We believe there are no rules that can justify the state or its coercive actions.
However, the statists who claim to rule us are in thrall to the myth of the constitution's legitimating power. Of course they get away with a lot that any plain reading of that document prohibits. This is the origin of "loose construction" in the first place: if they could just ignore the constitution to get what they want, they wouldn't bother framing their acts in any construction of the constitution at all. Clearly, the constitution doesn't matter to them in the way it's supposed to, but it does play some sort of role in the state's performative exercise of authority and power.
So we have a situation where the proper homage and respect must be paid to a document that provides the basis for the ruling class's state power. However, that class doesn't always agree about how that power should be wielded. When such a disagreement occurs, it can threaten the continued coherence of the state, which would deny the entire class uninterrupted power and legitimacy and create a window of opportunity for competing narratives of how we might be ruled. There must be an arbiter to resolve this dispute to preserve the overall infrastructure of the state.
In the same way a papal decree arbitarily puts to rest a matter of theological contention within the Catholic church, the Supreme Court can resolve a dispute among the statist political class in a "final" manner. Since the constitution replaced the Articles of Confederation to serve the business class's interests in "interstate commerce", the Supreme Court was designed to resolve disputes between the states in a binding manner. That does have implications for how the government will apprehend us, the people. It doesn't make that binding finality "legitimate" or "just". It just means that to the extent the government operates according to internal rules and policies, we can study its deliberations to gain insight into future encroachments.
Think of anarchist constitutional scholarship as counter-intelligence and strategic analysis. For example, the CIA was intensely interested in the internal disputes and intrigues of the Soviet Kremlin. This wasn't because they were rooting for one side over the other as a matter of justice or morality. It had more to do with trying to predict future policies and acts of that government, since those in charge are the ones who effect those policies and actions. Any interventions by the CIA in this area would have been in service to realpolitik, solely to advantage the U.S.government's interests.
I suggest anarchists think about constitutional law in a similar way. There may be broad, abstract principles of justice and reason embedded in the constitution. But they have little to nothing to do with how the state realizes its own power. We consider the exercise of that power to be a problem regardless of its adherance to an over two hundred year old document. So we should try to predict the political zeitgeist and foresee threats to ourselves and our communities, analyzing these matters in cold, calculating terms rather than in an outraged, indignant matter. Constitutional scholarship has something of a rhyme or reason to it, and it might be helpful to understand as a rear-guard defense against the state while building our own autonomous institutions to meet our needs.
To flip von Clausewitz's aphorism, politics is the continuation of war by other means. Anarchists should regard constitutional politics as nothing less. Obamacare is just another move in the chess game between privilege and the people. The solution to its injustices is not to convince the ruling class that its own myths allow us a bit more freedom; it is to topple our rulers and their myths utterly, building our own solutions, discovering our own sources of transcendent meaning, and defining the legitimate in our own interests. The constitution is of no help there except as a kind of specification document for one of the enemy's weapons.