Narrowing Miranda?

Normally I am all for civil rights, and oppose any decision that increases the power that authority holds over individuals. The recent Supreme Court decision that supposedly “narrows Miranda rights,” however, seems to me like a perfectly proper decision. I’m looking at this from a standpoint purely of logic, as I know nothing about it whatever from a legalistic standpoint. I’m merely saying that I don’t find it very disturbing unless someone can show me otherwise.

A guy named Thompkins was arrested on suspicion of shooting someone and was read his Miranda rights before questioning began. “You have the right to remain silent, and if you give up that right anything you say can and will be used in a court of law,” etc. The questioning went on without the guy asking for an attorney and, for the most part with the guy sitting mute. From an article in The Detroit News,

When police questioned Thompkins, he remained mostly silent for more than two hours, Jacobs said, but he later answered "yes" when one of the officers asked him if he prayed for forgiveness for "shooting that boy down."

He was convicted on the basis of that answer and his defense claimed that his Miranda rights were infringed. The Court upheld the conviction, claiming that he could have ended the questioning by asserting that he was claiming his right to remain silent. Justice Sotomayor was in dissent, saying that the decision “turns Miranda upside down," but I’m not sure at what point she expects the police to stop questioning a suspect if they do not say that they are asserting a right to silence.

They bring a suspect in, read him his rights, he says nothing other than that he understands his rights, and they begin questioning him. Then what? He either answers or he does not. If he is not answering but does not tell them he is “asserting his right to silence,” what are the police supposed to do?

It seems to me that accompanying the right to silence is the obligation to claim that right by asserting it, or at least by actually remaining silent. If the subject has not “asserted the right to silence” and has acknowledged his right to not answer questions, then if he chooses to answer a question how can that answer not be used against him?

Certainly it would be true that sitting in silence while police are hounding you with questions would be hard, but at what point are the police required to stop asking questions? Two hours is rather long, but does not strike me as unreasonable given the gravity of the suspected crime.

The defense does not claim that Thompkins was being tortured, or even coerced. They do not claim that he asserted that he was not going to answer questions, that he asked for an attorney, or that he even asked that the police stop questioning him. In fact, throughout the session he was apparently answering some of their questions. Why would the police stop asking questions?

Certainly the rights of individuals must be rigorously defended, but Justice Sotomayor's position would seem to imply that police may not question suspects at all. If we expect law enforcement to protect society we cannot tie both hands behind their backs.