I think people should get life sentence if they murder, because it´s always possible that the judge or the jury is wrong.
A lot of people have been executed for felonies they didn´t commit.If they were still in prison and they got a life sentence for a wrong punishment at least they had the rest of their life.
No judical system is foolproof, i don´t think that there are a lot of cases where it was absolutely clear that one commited the murder.
If someone has to spend the rest of his life in prison his life is taken away as well and they don´t endanger anyone while they are in prison.