"Some are born with no lights at all in the Sympathy, Empathy and Caring department."
Lizzie, you appear to be re-inventing human anatomy to create a new born-a- monster' species; sorry - such creatures are formed by personal circumstances and not born - Ray Bradbury fantasized them brilliantly in a couple of his short stories.
"they should have been kept away from the public until it could confidently be shown that they were not a menace to society."
And presumably it was judged that they were - I don't believe that the crimes committed by Venables, which he almost certainly picked up while incarcerated, counts as failure. If he were to continue with violent criminal activity, that would be a different matter and would be presumably acted on by he authorities. Thankfully Britain doesn't operate a three-strikes-and-you're-out, as does America.
Nothing that has been put forwards here persuades me in any way that this, or any other case should be taken out of the hands of those responsible and put in the hands of what is essentially a vigilante (even lynch) mob.