Spot on! Most americans believe that race, culture and ethnicity are clearly and strongly defined (and that they are simple facts rather than social constructs).
When spending time in the US I find myself experiencing double consciousness, asking myself if I fit into the stereotype that people have of me.
A case in point: in many sitcoms over the last 20 years you can find the same cliches around a white person trying awkwardly to say something without sounding racist.
This! In history, a lot of racism has been created to justify wars, economical exploitation, slavery, creating political scapegoats and so on.
Demonizing an enemy is the most basic method to polarize people. This type of "psyops" was extremely common during WW2.
People often don't really want to look at the root of racial, ethnic, political discrimination because it has to do with economic and political power.