Let's imagine a world where everyone is good and they do good acts. They are brave, save lives, give to charity etc. Now since all humans are not the same, it is only natural that some are better at these good acts than others. Maybe they are braver, stronger, faster, smarter than others.

Suppose you are one of the "others". That you are not good at being good. Thus you do not get the necessary positive feedback loop by doing these good acts. You are ignored. You become unfulfilled.

The point that I am making is that there isn't a place in the world for ALL of the good people, just the excellent ones.

So where does that leave you as one of the "others"? Should you continue your life as a non playable character doing and saying all of the right things, with none of the reward or maybe......you should stop trying to be good. Maybe it's time to be the bad guy with bad intentions.

This is where the seeds of evil are being planted.
See this scenefor a visual and similar story to the one that I have just conjured up.

In conclusion, yes there are bad people out there with bad intentions. They do it because the world has enough heroes. So being good will not give them the dopamine rush, the satisfaction, and the fulfillment they desire. They must seek evil.