Why was 21-year-old Dzhokhar Tsarnaev sentenced to die in a state so generally opposed to capital punishment? A recent Boston Globe poll found that only 19 percent of Massachusetts residents wanted the Boston Marathon bomber put to death. The state hasn’t seen an execution since 1947.

That sentence happened because national politics took the matter out of local hands. The federal government forced a death penalty trial. Only those open to a death sentence were allowed to serve on the jury. That made the jury members unrepresentative of the local population and the outcome preordained.

The sentence has eroded a sense of unity — the notion that a community can stand up to an awful crime without compromising its moral objection to capital punishment. And it goes against national trends.

Americans’ support for the death penalty has sharply declined. Not long ago, about 80 percent of the American public favored it. A poll last year found 52 percent preferring life behind bars over execution.

Even some conservative states, such as Nebraska, are witnessing serious moves to end the death penalty. Opposition takes several forms: That capital punishment offends the pro-life ethic — as forcefully stated by Pope Francis. That executing someone who was wrongly convicted is an unspeakable horror. That the drawn-out and expensive appeals process typically following a death sentence serves no one, including the victims.

A discomfiting oddity of capital punishment is that whether and how it is applied depend on the place. The flamboyant cruelties of the Islamic State’s beheadings and the antiseptic lethal injections in death penalty states seem variations of the same thing.

In 2008, the Nebraska Supreme Court ruled the electric chair unconstitutional. The current debate includes the shortage of drugs for lethal injections. These are discussions one shouldn’t want to have.

Many Americans, Bostonians included, remain adamant that criminals like Tsarnaev need to be eliminated, without much concern for the means. “I don’t think there’s any punishment too great for him,” Boston Mayor Martin Walsh said after the sentencing.

And some who generally oppose the death penalty say they would make an exception in the case of terrorism. They describe the Tsarnaev brothers’ rampage as more an act of war than a multiple murder.

We must question, though, whether by defining a heinous crime as a politically inspired act, we are further inflating already-grandiose misfits into historic figures. Fears that executing Tsarnaev will elevate the former college student into martyr status are not unfounded.

That his twisted admirers might respond with violence should not be a concern in meting out justice. Let that be said. But how much more diminished Tsarnaev would be if he were simply stored behind bars with the serial rapists and the holdup men.

The gruesome pomp that would surround a Tsarnaev execution could further move the marathon bombing focus from the crime and its victims to the criminal. That helps explain why some of the affected families have opposed a death sentence.

Bill and Denise Richard, whose 8-year-old son was murdered and whose 7-year-old daughter lost a leg in the bombing, have been among them. “For us,” they wrote, “the story of Marathon Monday 2013 should not be defined by the actions or beliefs of the defendant, but by the resiliency of the human spirit and the rallying cries of this great city.”

In sum, they don’t want Tsarnaev made more important than he is.

The marathon’s finish line, once a place to leave flowers, now evokes more complicated emotions. But the society that suffered the carnage did not have a say in the sentencing. That is one consolation for those Bostonians pained by the outcome.

Froma Harrop is a syndicated columnist. Follow her on Twitter @FromaHarrop. She can be reached by email at: fharrop@gmail.com.