Great answer and examples above. Here are some additional ones to consider as possible thesis statements:
* The death penalty is too expensive and time consuming to effectively prevent people from committing murder.
* The death penalty is a necessary punishment in the age of terrorism and serial killers, as society has a right to protect itself from the most violent of criminals.
* As most if not all murderers are clinically insane, the threat of the death penalty does little to stop them.
* The death penalty satisfies the biblical principle of "An eye for an eye", and is as close to justice for murder victims as we can get.
This would depend very much on what you intend to say about the death penalty. I can imagine you would have some very different thesis statements depending on what your opinion is or what you are trying to say about the issue.
- The death penalty is an outdated punishment that is only used in countries with backwards legal systems.
- The death penalty is a just punishment for horrific crimes. Countries that do not use it coddle their criminals.
- The death penalty is the only way to deter people from committing terrible crimes.
- The death penalty does not work to keep people from murdering each other.
- The death penalty cannot possibly be administered fairly and must be abolished.
- The death penalty is necessary so that people in a society will feel like justice is being done.
It occurs to me that it might not be necessary to start with a thesis for or against the death penalty after all. Judgiing from my own thoughts and feelings, it would be hard for me to come out with a thesis statement that the death penalty should be abolished or that it should be retained. I simply don't know. It would be easy to say that the death penalty should be abolished because it is cruel and unusual punishment, because it is unfair to minorities, and because it doesn't deter capital offenses. It would also be easy to say that cold-blooded murderers don't deserve any consideration and that they ought to be eliminated--especially for such atrocities as torture-murders of women and children.
Another approach to a thesis statement therefore might be to state that the death penalty poses a moot question which has yet to be satisfactorily answered. Then the follow-up would be to present the arguments against the death penalty and the arguments in favor. (And there are plenty of people who favor retaining the death penalty and even using it more often.)
This would be a more difficult essay to write, and the conclusion would also be difficult to formulate, but many studies end with the time-honored, all-purpose conclusion that the problem needs further study. After all, your opinion is only one of millions, and your essay is not going to affect the death penalty one way or the other. The same would be true for me if I were to write an essay on the subject. I really don't know. I'm not crazy about the death penalty, but there are many cases I read about in which, to be honest, I certainly can't feel sorry for the person getting the lethal injection.
Any thesis statement should be determined by what the author really believes. This question about the death penalty is one that really tries to force the author to take a position for or against. It should be very easy to defend either position. For example, execution obviously gets rid of criminals and prevents them from committing further crimes. On the other hand, it has not been proved that capital punishment reduces crimes. You have to begin by asking yourself what you really and truly believe, and then try to persuade your reader to believe the same thing.
My advice to you is to decide, from within, whether or not you are for or against the death penalty. Make a list of reasons why you are for or against it, writing the strongest reason(s) first. Your thesis statement will come to you.
I also suggest that you argue the opposite way as well. Make a list of reasons regarding the other side. Don't hold back. Argue just as vigorously for the other side. This exercise will help you defend your own position much better (believe it or not). It will also strengthen your paper by helping you include what are called "concessions." It strengthens your arguement and essay overall by its presentation of a well thought out, dispassionate, cogent, and intelligent piece of writing. Run this answer by your English/Writing instructor(s). I'm sure they'll back me up.
Well wishes on your endeavors!