Why is someone like that?

Are they not just by-products of our society?

Should we not be looking inwards to try to find out what characteristics of society lead a small number of individuals to become phycopathic criminals and the like?

Executing the 'sicko' might give us a sense of justice and revenge but it doesn't really address the problem of why he was like that in the first place. Indeed, it does nothing to prevent other people like him re-offending (as they are phycopathic and think with warped logic).

As far as prisoners are concerned generally, the idea (and I know we are far from achieving perfection) is to re-habilitate criminals so that they can (eventually) resume their place in society amd then you won't have to keep paying for their benefits.