What's your definition of someone who is unstable or do you call a person unstable because you don't understand them?

In reality, people are different to each other in many ways such as personality, views, the function of their brain and personal philosophy. It bothers me that there are people in the world who like to label each other due to being stereotypical and ignorant. If people manage to accept each other's differences, there would be no ignorance, intolerance, hatred and anger but unfortunately in the real world people are like that. I think that when someone labels a person as unstable, they are just being a control freak because they expect that person to fit in their mind so when they come across someone who has a different mindset, they will expect them to stoop to their level. When the person who is being labelled does not conform with the other person's expectations, they will be seen as emotionally unstable or unstable in the brain. I think that some people's erratic thinking is from an after effect when they've been wronged psychologically speaking by another person who would be a psychological bully.