At the Democratic debate on Thursday, Hillary Clinton and Bernie Sanders had a candid debate on the death penalty — a debate that's just not common at the national level.

On the side for the death penalty, Clinton argued that some crimes are so heinous that death is the only proper punishment — while arguing that some states are too shoddy in their use of the death penalty:

I do reserve it for particularly heinous crimes in the federal system, like terrorism. I have strong feelings about that. I thought it was appropriate after a very thorough trial that Timothy McVeigh received the death penalty after blowing up the federal building in Oklahoma City, killing 168 people, including 19 children in a day-care center. So I do for very limited, particularly heinous crimes believe it is an appropriate punishment. But I deeply disagree with the way that too many states still are implementing it. So if it were possible to separate out the federal from the state system by the Supreme Court that would I think be an appropriate outcome.

On the side against the death penalty, Sanders said that the government simply should not be involved in executing people, especially since it can get things wrong:

I hear what the secretary said, and I understand her. There are, all of us know, that we have seen in recent years, horrible, horrible, horrible crimes. And it's hard to imagine how people can do, bomb, and kill 168 people in Oklahoma City or do the Boston marathon bombing. But this is what I believe — and for a couple of reasons. Number one, too many innocent people, including minorities, African Americans, have been executed when they were not guilty. That's number one. So we have to be very careful about making sure about that. But second of all, and maybe in a deeper reason, of course there are barbaric acts out there, but in a world of so much violence and killing I just don't believe the government itself should be part of the killing. So when somebody commits, when somebody commits any of these terrible crimes that we have seen, you lock them up, and you toss away the key. They're never going to get out, but I just don't want to see government be part of killing. That's all.

The exchange between Clinton and Sanders shows that this is mostly a moral, ethical argument. We can look at statistics all day about the high cost of the death penalty and how at least 4 percent of people on death row are innocent. But at the end of the day, it largely comes down to whether someone believes some crimes are so bad that only government-sanctioned death is a proper punishment, and whether or not the government should be killing people.

Still, it's worth noting that Sanders is closer to the Democratic base here. A 2015 Pew Research Center survey found that while support for the death penalty has dropped among all party identification, the sharpest decline has happened with Democrats — 56 percent of Democrats oppose the death penalty.

Perhaps that's why this is an issue that can come up at debates at all now. Just a few decades ago, after all, both sides of the aisle were passing laws that strengthened the death penalty. Today, at least Democrats disagree with the government executing people.