I don't know anymore.

So I was watching some show talking about serial killers.
And I got really cought up in it.
I analized those serial killers' actions and
I came up with the fact that most of them are
sociopaths. But that's not what i came to talk about.
Me and a friend where having a conversation,
he proposed the idea that all criminals should be killed.
Specially serial killers.
And I didn't know whether to agree or not.
I believe that serial killers or any type of killer is just a sick person.
It comes from their childhood and if they are
raised wrong they can't really do anything about it.
But then again, they killed people so..?
What's the right answer?