Human beings are racist by nature.
By "racist" I mean, we are genetically prone to be biased toward those physically different than us.
This is why in nearly every high school across the country, white kids tend to fraternize among whites, blacks with blacks, and hispanics with hispanics.
There are two types of racism: a natural inborn tendency to segregate or be biased, and the other which is actively and willingly despise and alienate others of a different race.
This is why you can never eliminate racism, but steps can be taken to mitigate and hopefully suffocate hate-fueled racism.
Keep in mind that humanity is corrupt by nature. That is an inescapable reality.