Earlier quoted context omitted.
Emotional responses shouldn't trump your sense of justice and fairness to human life. I have someone that was close to me murdered and I don't think that a harsher punishment only for my enjoyment is the answer to "what is justice?".
hypothetically, if you could see into the future and ascertain that the perpetrator feels regret and would never commit another crime, should they still serve time? I would think that there should still be some period of incarceration as a putative measure.
If an individual is dangerous for society they shouldn't be in it, this doesn't mean forever if there is a possibility of rehabilitation. There are many monsters locked up that probably should never be released, in that sense the justice systems of Norway, Germany, Sweden and others work well: you are locked up to 20 years, after that your case is reviewed and if you are still deemed a danger to society you get it prolonged, a few times this goes on for life.