What can one say in the argument over capital punishment that hasn't been said before?

Perhaps only that the case is not one-sided and that both supporters and opponents typically play fast and loose with the evidence. Let us dispense, for now, with the unrepresentative horror stories of vile killers who were never executed or sympathetic defendants convicted with insufficient evidence.

I generally support the state's seriously considering taking the life of those convicted of committing first-degree murder or worse. It is indisputably an effective, and arguably valid, way to protect society from the most heinous criminals who commit the most atrocious crimes — those for whom it is reserved.

Much of the problem in the debate is the disingenuousness of some who argue against the death penalty. Those who maintain that the punishment ends up being harder than life imprisonment on the victims' relatives and loved ones ignore the fact that it is the seemingly endless, stressful and legally complicated waiting period — not the execution of the murderer — that is the source of the pain.

Similarly, those who argue that the death penalty is more costly than life imprisonment selectively ignore the price of maintaining the perpetrators. As Dudley Sharp, one of the most thoughtful death penalty supporters, has argued, such estimates use rhetorical tricks in focusing on the up-front costs of the death penalty, ignoring the long-term costs of life without parole. Regardless, the monetary savings, whether real or imagined, are not sufficiently important in matters of such moment.

The likelihood of the death penalty deterring capital crime (opponents claim it indisputably does not) has been misrepresented as well. It is impossible to measure, through controlled means, how capital punishment is a deterrent through estimates of how the infrequently used instrument reduces capital crime. When, in many states with capital punishment, execution is delayed for decades or seldom used, most murderers anticipate they will not die for their crimes.

As columnist Jeff Jacoby wrote years ago in The Boston Globe, between 1965 and 1980, when there was virtually no use of the death penalty in the U.S., the number of murderers exploded, only to decrease as executions became more common.

Maryland provides for the death penalty but does not currently implement the death penalty. Theoretically, it may be utilized only, as The Baltimore Sun summarized, "for murders in which there is DNA or other biological evidence that links the defendant to the murder, a videotaped confession or a video recording of the crime."

By focusing on acceptable evidence, such requirements provide killers a roadmap to avoid capital punishment: avoid leaving DNA evidence, do not confess under any circumstances, and do not kill anyone near a camera — or just order (orally, of course) someone else to kill the intended victim(s).

Racial bias, often cited as an anti-death-penalty argument, is a complicated matter. Most reasonable people do not want a perpetrator's race deciding his penalty. But a Rand study and even the well-respected Paternoster study in Maryland found that the race of the murderer had no significant effect on the use of the death penalty (from Paternoster: "there is no evidence that the race of the defendant matters at any stage once case characteristics are controlled for") but that the race of the victim systematically affected handling of cases. Racial biases in use of the death penalty, wherein demonstrated, should be eliminated. But this does not argue for eliminating the penalty; it argues for eliminating the bias, if and when it exists.

That brings us to the only dispositive argument against the death penalty, one raised recently in the high-profile case of Troy Davis: the possibility of executing an innocent person. Those who claim that the state has executed "innocent" (when they should say "legally not guilty") people generally refer to the fact that people have been convicted despite the inadequacy of the evidence.

Let us concede that, historically, there have surely been cases wherein people have been executed who simply didn't do the crime for which they were put to death. That is a daunting realization — but so is the realization that convicted lifers have killed again while serving their sentences. While it is ethically difficult to trade the life of even one improperly convicted person for the lives of others yet unknown who might someday be killed (or ordered killed) by an incarcerated murderer, certainly there is an argument for the death penalty in the case of murders committed by prisoners already serving life sentences. If not, what deterrence against murder is there for a lifer?

It's not an easy decision to make — contrary to death penalty opponents' claims — but three of the classic purposes of punishment are incapacitation, retribution and deterrence of criminals and criminal behavior. Rehabilitation, the other oft-stated purpose, should take a back seat in capital crime.

Let's continue to improve, but judiciously use, the death penalty.

Richard E. Vatz, a professor at Towson University, is author of the recently released "The Only Authentic Book of Persuasion." His email is rvatz@towson.edu.