“There are two kinds of people in the world: those who say there are two kinds of people in the world, and those who don’t.”
Of course, there are far more than two kinds of people in the world. There are certain times when simplifying the complex is the right path: equations in math and physics, art, universal principles, spiritual truths. This is the path of distillation and purification.
There are other times when simplification leads not to clarity and beauty, but obfuscation and confusion. Grey disappears and one is presented with a false choice between black and white. Right and wrong. Us and them. Ideology replaces real thinking.
When someone says there are two kinds of people, they may be offering you a helpful framework for thinking more deeply about human nature. It’s more likely the case that they are trying to stop discussion and reflection.