My middle name is misery

There are two primary motivations for declaring someone or something else evil:

• Enhancing the cohesion of your own group;
• Giving yourself permission to be evil "in retaliation".

We might therefore say that declaring others to be evil is the source of all evil. Because factually there is no such thing as someone beyond the reach of goodness. Hitler loved his dog. Margaret Thatcher was on the research team that invented soft-serve ice-cream.