"Before Kinsey rapists/childmolesters in America got the death penalty. " well the Kinsey reports were published in the 1940s.
Kennedy v. Louisiana held that the Eighth Amendment's Cruel and Unusual Punishments Clause did not permit a state to punish the crime of rape of a child with the death penalty; more broadly, the power of the state to impose the death penalty against an individual for committing a crime that did not result in the death of the victim is now limited to crimes against the state (e.g. espionage, treason). Yes, it was after Kinsey, but I don't see the relation, as this was a 2008 case. In a similar vein, before the moon landings, child rape was punished by death and now it's not, but it doesn't have anything to do with the moon landings.
As far as I know the vast majority of sex offenders under ‘psychopath statutes’ of the Depression and McCarthy eras got lifetime mental hospital commitments, especially white middle class offenders that could be treated with a variety of experimental techniques. For blacks accused of raping white women, yeah, the death penalty in some cases may have taken over as Southern lynching laws started to fade out.