Wow, that's true double-moral.
No, that is not something that needs to be done. The rapist have done something incredibly bad, but killing him in revenge is just as bad. Even if he's a rapist he probably have someone who loves him.. family/partner, whatever. They will then feel the same sorrow.. should they be allowed to kill the father who killed their love? Rollercoaster.
And even if the rapist is a lonely person who noone loves, he should not be killed. The killer (the father as you wrote) is just as bad if he does it. The rapist should be punished within the frames of the law. If the father kills the rapist, the father should be punished within the frames of the law.
One terrible act can't allow another terrible act to be accepted.
i disagree with the idea that it is never okay to take a human life.
1. if someone has battled an illness, and continued treatment would be torture... the person should be allowed to end their life. with their family present, with their choices respected.... the transition should be peaceful and dignified.
2. self defense.. if you try to kill me, i will try to kill you first. so the "never right to kill anyone" is rendered null.
3. how many people did you see crying out that killing Osama was wrong? in that instance most americans seems to think killing another human being was pretty damn nifty.
in the case of kiddie raping asshat. the law, any sentence or punishment, would fail to prevent further assaults. jail terms for rape/child sexual assaults are embarrassingly short. there will always be a chance he might get out, that he might not be convicted either from police error, idiots on the jury or statues of limitations.
and realistically, sentencing a child rapist to jail is a death sentence... man with gun just saves the local tax papers 3 million dollars.
as far as his loved one.. grief counseling and therapy should be made available. just playing the numbers one family grieving is better than hundreds of damaged families and wounded children.