He got 20 years for killing his girls baby. He's laughing in her face in court. Are you going protest if he gets beat to death?
You are missing the point again.
Who is going to beat him to death?
An agent of the government? Do you want government agents who live among us, who raise children that play with our children, to be given the power to beat some people to death?
Prisoners? You want extrajudicial murderers to be released to the public?
The guy could have killed 100 babies. Sentence him to a life in prison, I don't care. If he acts up, put him in solitary and/or maximum security. Send him to Alcatraz.
However until he dies he is a citizen and has certain rights that should not be violated by any well meaning government or associated entities. Those rights include the right to not be extrajudicially executed or tortured. It's not about the evil of the prisoner.