"They felt that their evil acts, even if much worse than those of others, were going to be forgiven..."
Yes, that is almost right, but for one detail. If one does not believe in God or an afterlife, there is no fear of doing wrong so long as every mortal around you is deceived into thinking you are righteous and your victim deserved his beating. That way, if the issue of forgiveness ever comes up at all, it is on the parts of the idiots (some of whom witnessed or even participated in the beating), who demand of the victim that he forgive his assailant. In this clime, not even the good Samaritan is safe, for the crowd-controlling "nazi" will convince everyone that the Samaritan is "giving aid and comfort to the enemy."
There is a verse in the Wuest expanded translation of the N.T. in which Jesus states that the two highest callings are the love of God and the equitable administration of justice. Much attention is given to the former and almost none on the latter. If one wrote a sermon on that subject, one could work in this quote from Einstein:
"The world is a dangerous place to live; not because of the people who are evil, but because of the people who don't do anything about it."