Saying "racism is stupid" or something like that tells you are a brainwashed idiot.
"Racism" pretty much means that you care more about people that look like you or are part of same culture, language group etc. That makes perfect sense. You naturally care more about people that are your family or tribe = look more like you, have same culture as you.
"Racism" makes sense, because it gives better opportunities for you and your offspring. If you are part of privileged group because of your ethnicity or "race" it makes perfect sense to support "racist" ideology if it benefits you. It is pretty much same thing with political views. If you are poor it makes sense you support leftist economic views, because it benefits you and your family.
It might be that racism does not make sense anymore in countries that are heavily mixed. It can be bad for all if it causes great instability and violence in society. Also if your family is mixed - it makes perfect sense to fight against "racism".
Im just looking this thing (like all things) from purely factual point of view. I say "racism" is natural for humans and in certain situations it can make perfect sense for certain people.
From historical point of view I would say that opposite is true or at least your statement is totally false. Many "racist" societies have been very succesfull. (British Empire in 1800s for example was very racist and untolerant) I dont think there is really proof that tolerant societies are more succesfull. Many tolerant societies have been succesfull, many untolerant societies have been succesfull. I also would add that"tolerance" is really vague term.