Like many have said, you're confusing "Racism" with "Prejudice".
I am fully aware of the diversity and differences around me. And from experience, I have learned that people from a certain background, be it race (there is no such a thing as race, btw), natioinaility, personal upbringing, region they are from, religious beliefs etc. possess common characteristics. It's called cultrure. I may dislike a certain behaviour, and I may find that a certain ethnic group is more likely to possess this behaviour. But it would be wrong of me to catergorize all members of that ethnic group and say that all **** people do that. Even more wrong for me to dislike this group of people based on this knowledge.
When I see a person for the first time, I admit that deep within me there exists some preconceived judgement based on the person's appearence, but I don't let these thoughts influence me. These baseless judgements are either disputed or confirmed as I get to know the person.
You are talking about generalizing and lumping people in groups based on their race. I am telling you that this generalization does not only apply to someone's ethnic background. For instance, when you meet 2 people of the same ethnic background, and find that one of them is from the east coast, and the other from the west coast, you naturally form prejudices in your mind, based on your experience and knowledge of people from these regions.
The above is different from racism. A racist is a person who differentiates people based on their race alone, and despises people based on their race alone. This person puts people into classes, making one "race" more superior than another. He/she can be outspoken or quiet about it, but the person is a racist anyhow.