I think that if you look at the average sentence for manslaughter you would find less than 10 years.  Manslaughter as you likely know is causing death through violence but without malice aforethought.  Even premeditated murderers (all degrees), on average likely don't spend more than 15-20 years in jail.  Compare murder with a hand in the pants causing no injury beyond anger with the sentence for the latter in the same ball park as the former. Rational?