This week's Economist/YouGov poll found that "majorities of Republicans (77%), independents (66%) and Democrats (53%) still support the death penalty."
The poll also asked about whether people think innocent people have been wrongly executed and whether the death penalty works as a deterrent. Have a look:
most a plurality of Americans think innocent people have been executed and think the death penalty is not a deterrent. Are they right about this stuff?
It's hard to get conclusive data about wrongful executions because, as the Death Penalty Information Center puts it, courts "do not generally entertain claims of innocence when the defendant is dead." That said, there are a number of very questionable cases. And given how many last-minute exonerations there have been, it seems likely the death penalty has been misapplied.
The question of deterrence is murky, too. Amnesty International presents the chart below, which shows that states with the death penalty have much higher murder rates than states without it.
They take this to show that the death penalty isn't a deterrent. To be fair though, there are lots of ways to interpret this data. Maybe the causation goes the other way and people support the death penalty in these states because of a high murder rate. Or maybe southern states have the death penalty and more murder because they have a stronger "culture of honor."
At any rate, the fact is that people do believe it ends up killing innocent people and also that it's not an effective deterrent and they still support it. What's the point?