But I dont really think common sense is assumed to be true. I think that it's learned to be true. Does that make sense?
Like for example: A kid puts his hand in fire and it burns his hand. Well now, common sense would tell him not to put his hand in fires anymore because they'd get burned. He's now gained some common sense. Am I right?
I don't think there is a difference. Prejudice is "learned". Humans are very good at "learning" things without logic or reason. It is a bad habit if you assume something without thinking or questioning. It is an equally bad thing if you learn something without thinking or questioning.
As a kid I rode a bike and I fell and took banged myself pretty up pretty good. It hurt. By your argument common sense would tell me not to ride a bike anymore because I will get hurt. But I still went back to ride my bike and I still enjoy bike riding today.
The difference between your fire example and my bicycle example is logic and understanding. I didn't just learn an unquestioning fear of fire. I understand the certainty of pain putting my hand in fire, but more importantly I leaned the why and how. I learned when fire is safe and useful. I now know about heat and burning and I know that there is no benefit to sticking my hand in the fire while I learned to cook marshmellows.
I also learned that even though I may occasionally get in an accident on my bike (damn car doors), I know that I will likely not hurt myself seriously. And I know that my enjoyment is worth it.
In each case it is better that I don't avoid questioning and that I keep thinking and understanding. In any case logic and reason and understanding are sufficient. I don't need common sense.
Think about how easy it is to learn the wrong "common sense" from your experience. Racism is often based on things you see on television, or even specific experiences. Humans often draw the wrong lesson. Look at what has happened to Muslim American families who are decent people but are treated with suspicion or even cruelty because of what people "learned" by what they saw on television.