The concept of stereotyping has become closely linked with racism, bigotry, and prejudice in general, and as a result has become tainted with a bad reputation. But stereotyping is actually a fundamental part of the way our minds work. We subconsciously group similar things together and assign general attributes to them.
In terms of survival, this is a big winner. For instance, when we suddenly see something long and thin moving on the path in front of us we react immediately because it might be a poisonous snake. We don't take the time to first determine whether or not it really is a snake, and certainly not the time to determine what species it is. But in doing this we condemn the vast majority of snakes and twigs to a very unfair judgement.
Our minds do this continually, and we form generalizations of all kinds of things that can quickly be recognized, including other people's race, sex, and age. This is a completely normal and natural process and there is nothing wrong with it. We recognize something on the road first as a vehicle, then as a car, then as a Honda, and so on, going from most general to more specific as time allows, giving us the chance to react as quickly as possible when a fast reaction might be required.
But what we as intelligent and moral beings must also do, under circumstances where there is sufficient time to properly analyze the situation, is to continually monitor all such reactions, to question all thoughts that might have resulted from this process, and to assign an appropriate weight to the idea before making any significant decisions.
I myself grew up at a time when television and films were full of racial stereotypes, and the community I lived in did a good job of confirming most of them. Those images and thoughts are still with me and always will be. But what is important is that, whenever I think about something, I be aware of the sources of the various concepts and dismiss some of them as being invalid or insignificant.
Anyone that says they aren't racist, that they don't think that way, is only fooling themselves. The best we can do is to recognize our own (and other's) racist thoughts for what they are and to treat them accordingly.