It appears those who think it is cruel, confuse immorality with sin. Immorality might be sinful, but sin simply means missing the mark, not performing as God had planned or intended for the Creation.
It is true that sin is exceedingly sinful, and one of the primary reasons not to act independently of what He has provided is to avoid these types of consequences.
For those who don’t think the consequences are necessary, this present age is one additional testing of that same hypothesis advanced by the Adversary that he would make himself like the most high and could run the universe just fine without God. The issues of judging good and evil have not yet been completed, although the fallen angels have been judged.
Consequences for individuals should be based on the actions of those individuals, not based on the actions of the ancestors of those individuals.