Bennett believes that this admission negates what he calls the second most common justification for the death penalty. Of course, it's the second most common in some particular polls of the public, hardly the place to look for theoretical justification for capital punishment.
While Ms. Siegler believes that execution provides no closure in her experience, it may be the case that the death of the offender helps begin the process of healing for some people; there is simply not enough non-anecdotal information to make a judgment. So not even Bennett's premise is beyond question.
In point of fact, however, "closure," which I take to be the notion that the execution of a murderer will help heal the psychological wound inflicted on the victim's loved ones, has nothing to do whatever with why the death penalty is an appropriate and moral penalty for certain offenses.
There are, in a nutshell, two main justifications for capital punishment, as I've argued before:
1) "Just Deserts": for some crimes, only the DP adequately addresses the moral equilibrium upset by the offender; that is, the only congruent satisfaction for the death of (especially) innocent victims is the death of the offender.
2) Deterrence: other families might also suffer such crimes if this offender is not executed (i.e., he might be paroled, pardoned, escape, or kill in prison), and some, if admittedly not all, other offenders will be deterred from such crimes.
The first is what appeals to most people when they hear about particularly heinous crimes: the belief that some crimes are so vicious that mere incarceration will not adequately address the offense to society. This central justification for capital punishment will never lose its force, so long as murderers continue to violate the arguably most important value of civil society, the sacredness of human life.
The second justification, deterrence, is a corrolary to the observation that society has a primal right to defend itself from those who would attack it, and a murderer who is executed will certainly be deterred from killing again (specific deterrence); and generally, murder is deterred at the margins by the existence of capital punishment (general deterrence), as the preponderance of studies now show.
Mark Bennett is celebrating over something of little importance, since whether the death penalty coincidentally gives "closure" to this or that victim has no bearing on the justification for capital punishment.