Capital punishment

Nowadays in some states like Iran, Iraq and Saudi Arabia some crimes are punished with death penalty. In some other places such as Australia, France and Germany, capital punishment is not used anymore. In the countries where it is used, it is only applied when crime committed is very severe and the author is 18 years old or over although some countries still apply it to younger people.
 First of all, there are some crimes that deserve a harsher punishment than just a couple of years in prison. I believe that in those cases people should get a life sentence, but they should not be killed. People who are in favor of this penalty often argue that it is a good way of preventing future crimes, but so is life imprisonment.
 Secondly in some countries this penalty is used for minor crimes, not that they are not important, but not every crime deserves the same punishment. Killing someone is  not the same as selling drugs for example. So it would be better if the different sentences  varied according to the severeness of the crime and the worst punishment would be life imprisonment.
 Thirdly, judges may be wrong, it happened throughout history that they made mistakes and punished people for committing terrible crimes and they turned out to be innocent. Death penalty can not be reversed, but life imprisonment can. Although most of the times the judges are right, there is a margin of error.
Last but not least, it takes a lot of time to decide wether a crime is worth of capital punishment or not, and meanwhile nothing is done. This is because it is an irreversible crime and it takes more time for judges to think about it and decide. On the other hand, judges may decide an amount of years in prison and then change it.
 The United Nations and the international laws prohibit it because it is clear that loss of life is not a fair punishment. To conclude, no one deserves to be killed, no matter what they did. but they do deserve punishment. The way of teaching that killing  is bad, in my opinion, is definitely not by killing people. I believe that capital punishment is controversial because it punished murder by killing. It makes no sense at all.
Standard form:
Not all crimes deserve the same punishment.
Nobody deserves to be killed because it is a human right.
Judges may make mistakes.
Life sentence is just as harsh and it does not involve loss of life.
Therefore, capital punishment should not be legal.