Final answer:
The correct answer is demagogues, which refers to political leaders that manipulate public sentiment and prejudices rather than using rational argument, often leading to a threat to democratic systems.
Step-by-step explanation:
The sentence 'The evil comes from the leaders, the demagogues, the professional distorters of right thinking and right feeling' implies that malevolent influence often stems from certain leaders who exploit their positions to manipulate public opinion. The correct word to fill in the blank is demagogues, which refers to political leaders who seek support by appealing to popular desires and prejudices rather than by using rational argument. This is evident in various historical and contemporary contexts where charismatic leaders have used fear and emotional appeal to solidify their power, often by portraying themselves as the saviors from so-called evils.
In the context of the provided references, the term 'demagogue' aligns with discussions about the rise of populism, the dangers it poses to democracy, and the comparison of political tactics used by infamous leaders like Adolf Hitler and Joseph Stalin, who are known for leading through fear and intimidation. This term is used to caution against leaders who may use their influence to undermine democratic principles and manipulate the populace for their own ends.