Racism is about more than what people think, and very much about how they act and what they do.
In my opinion racism is based entirely on how the person thinks. A person who is racist must adopt the ideology of race to even be considered a racist. A person can be ignorant, create bad laws, and generate negative consequences, without even being an actual racist. A person can do it out of greed and simply use race to justify a power grab as I said before. A person in power may use race ideology to divide the people out of power as a means of justifying their own position of being in power.
For example an old white male could use race ideology to justify why white people such as himself deserve to be in power. Suddenly it's natural law and justified by something such as IQ, or by God who for whatever reason chose him for divine rule. If you look back at history you will find that royalty used these similar justifications (God says I should be in power). Then of course these individuals promoted Christianity and religion as this helped them to maintain and justify their position of power.
Racism helps certain people to justify the unfair advantages they may be receiving. This goes on both sides actually because you can be of any race and receive an unfair advantage merely because of your race. The point is that in a world without race ideology then everyone should be given a fair chance without any group being given an unfair advantage due to perceived stereotypes (Blacks good at sports, Asians good at math, or whatever).
In terms of History of the United States I am well aware of the past. I'm more interested in how do we change the future. We agree race ideology is a bad idea so what can we do about this? Certain people will seek to benefit from any ideology that is in place to maintain or grow their power. This is true of religion, ideology, etc where if a certain religion is popular in a part of town then the politician may befriend the priests/monks.