"以良心为由而施加的残忍行为，是道德家们的一大乐事。这就是他们发明地狱的原因。"

Simplified Meaning:

People who think they are very moral or righteous can sometimes take pleasure in being cruel because they believe they are doing it for a good reason. When someone is convinced they are right, they might not feel bad about causing others to suffer; in fact, they might enjoy it because they think it serves a higher purpose. For example, in history, there have been people who justified torture or harsh punishments because they believed it was for the greater good or to save others from evil. The idea of Hell is used here to show that some moralists might feel satisfied with the idea of eternal punishment for those they consider wicked. This harsh approach shows how people can sometimes use their beliefs to justify harming others. To avoid this, it's important to question our own actions and consider if we're truly being fair or just using our beliefs as an excuse to be unkind.