Racism as it is called today is far different from what it was known as decades ago.
That said, in order to look clearly as this, we need to take out the human element, since we tend to muddy the waters a little too much. Lets take a toad and a Bullfrog. They co-exist, but rarely, if ever, mate or "hang out." Why? Because of the purpose of life itself.
What is the purpose of life? Well, on an individual scale, the purpose of life is to procreate in order to further the species. Effing duh, right? Now, in order to further the species, a specimen chooses a mate based on their preferences, which are based on a predetermination created by environment and up-bringing. Then, of course, doing the deed.
Not wanting to "hang out" with, be with, or procreate with those different is culturalism, and is perfectly natural and a fine disposition. Wanting to "be rid" of those unlike you is racism. It really is that simple.
Tell the fam to quit thinking politics, and start thinking biology. It makes things easier.
EDIT: sorry for the spoiler to those seriously searching for the purpose of life.