Why are religious fanatics the most inhuman people according to this teaching?
Religious fanatics are called most inhuman because they prioritize their religion's victory over the welfare of its victims. They are willing to torture, punish, and even kill those who disagree, showing no concern for what happens to them as long as their religion comes out on top. This teaching cites Saul/Paul coercing believers to blaspheme and persecuting them to death.
Les explains that Saul of Tarsus, before he became Paul, admitted he had received authority from the chief priests, voted against believers, punished them often in every synagogue, and compelled them to blaspheme. He forced Jewish believers to renounce their faith in Jesus, by threat of torture or whatever, all in the name of his religion. Les says there is nothing more torturous or more inhuman than religious fanatics, because they could care less what happens to their victims as long as their religion comes out on top. Saul was no different: he was exceedingly mad against them, persecuted them to strange cities, and went to Damascus to drag believers bound back to Jerusalem for trial and death.