OP, this question may be worth x-posting to /r/AskAnthropology or /r/AskSocialScience

What do you exactly mean by that? There have been several states or state-like entities who were very much founded on anti-discrimination. Probably not every individual upheld those beliefs. Do you mean something like that?

Whoever said that to you is a bigot, in the sense that he is looking only at the parts of the issue that support his prejudices. It just happens that it's currently fashionable to remember only white people abusing non-whites and enslaving blacks, and exclude the facts that don't fit this narrative. Every society has taken its turn as both the master and victim. Not justifying, just understanding.

A good window into this is to look at the names we have for peoples around the world. Every ethnic group's/language's word themselves means 'human beings' (Hutu, Cheyenne) or 'people.' Everyone else was something less, often 'not people.'

Both names for Germans, 'Deutsch' and 'German', come from Celtic, and were originally terms of abuse. 'Slav' is the origin of the word slave, because that's what their Viking masters thought of the Russians. 'Barbarian' comes from the sound of people who can't speak a civilized language, and the Russian/Czech/Polish word for the Germans is nemec, meaning, 'they can't talk.' Many of the names Americans have for the original inhabitants (Sioux, Apache) are the abusive names given to them by their neighbors. During the Soviet Union period, when everything was supposed to be equality and progress, Russians regularly referred to their ethnic minorities as 'black asses' (cherno-zhopy). Some modern Chinese government supporters use the term 'Han traitor' to describe someone who isn't loyal enough (Han is the ethnic group, not the government).

Some modern societies have tried to leave behind the practice of discrimination, such as the Scandinavians. Please remember that these are the former Vikings we are talking about, and that they were renowned for brutality and slavery. Even after the Viking period, look into the Swedes' behavior during the 30 Years' War, in which 1/3 of northern Europe died fighting over being protestant versus catholic.

All of human history seems to be "our team versus their team," and there is no substantive evidence showing that any society/ethnic group/civilization as a whole didn't act otherwise. Tiny groups of people who act differently are outliers; show me a black Quaker, and I'll reconsider my opinion. We should strive for a better future, but we shouldn't lie to ourselves about the past.