No one have the right of take the live of anybody, but what do you think is the most way to stop the criminal's who is accustomed to killing or raping? 
 the bad sistem of justice of many countries, make people think about this often and they look this like a way of resolve that big problem, since most of the time only  put them in prison for years does not solve anything but convert this in a school of crimes for them (Like in my country).
This method is failed when is executed an innocent person (as a boy said on the first page of the post) or when is used in wrong way.
But yes, i agree in part with this, because is necessary...