I actually see this argument a lot so here are my opinions about it:
Well I think a person can express a different feeling in different places, like when you’re in an argument with your family, you feel angry. But most of the time when there isn’t an argument or something that makes you angry, you feel neutral and others also see it. This way they might bring this bad or good side talk.
But you can’t expect someone to feel happy all the time. Is OK to be sad in a funeral because someone you loved died, and that’s where you express a different feeling rather than a sad side.
So lets say you did something really bad like murder, a person doesn’t do that for no reason or for having a good or a bad side, maybe the person is going trough rough times or maybe even has mental problems.
In conclusion, I think people have different feelings rather than good, happy, bad, sad, evil sides. I think this should stay on movies and drama films rather than real life.