There is no room for some libertarian free will talk here. Regardless of one's choosing, US does not prohibit traveling to Iran. In fact, it's prevailing that Switzerland is interim de-facto protection power over US interests in Iran, so the point is moot.
But to point out how "useful" one can be in situation like this without de-humanizing anyone regardless of nationality, we have to consider some facts here. Is Amir Mizra Hekmati a US spy? As you may well know and as many people do, clandestine operatives are anonymous and are not in business of becoming a collateral damage. Matter of fact, most of us just don't know, can't know, won't know and don't have to know, because nobody needs to know. And those are the facts we are dealing with.
So what if he isn't a spy? Then one must think about why Iranian gov't is boasting and carrying out "court prosecution" of an innocent person. Of all places, state controlled media in Iran, what is the point of all this propaganda?
Even if Amir Mizra Hekmati is a silent partner in NCS clandestine effort, how much credibility in the region will US lose in the wake of so called "Arab Spring"? Or better yet, should US care? What context is this leading US into? Is this even relevant?
Now here comes the point.
Iran wants... no, Iran IS taking this opportunity to boost its regime's influence and credibility over neighboring region during this turbulent time. Amir Mizra Hekmati is just a pawn caught in the middle. If US doesn't do anything as some suggested we take "Don't Do Something, Just Stand There!" approach, we can be assure that Iran will bank on every opportunity to takeover US influence in the region. And in the back of my mind (small mind at that!), I think, Iranian gov't is playing a game of double jeopardy with US; damn if you do, damn if you don't.
Therefore I think, US should be in damage control mode to minimize any further erosion and get back to negotiation. To do that, we may need to rollback some of recent Obama's Iran Econ. Sanction executive orders if need arise. After all, what does Iran have to lose as the recent intel shows that they already have nuke bunkers anyway? By killing US interest during negotiation, Iran has everything to lose, including credibility.