Frankly, I think your teacher is a fool.
Racism comes from two sources - real and politically-charged.
Real: Anybody who lives in a town with a mix of races knows racism is real. They can see how whites and blacks treat each other.
Politically-charged - Contrary to what your teacher said, the media doesn't promote racism to keep whites from seeing what they have in common with minorities. The media, and typically liberal politicians, promote race hatred or "class warfare" because that strengthens and promotes their own power agenda. Politicians score big points by
claiming that Government needs to "help the minorities". In some cases, this is true, but frankly, in many cases it is not. No matter - promise to pass bills and policies that will funnel money into minority assistance, and you can guarantee pulling in large blocks of voters.
The media love to report on trouble, on the downtrodden, on the oppressed. So they love to make hay out of racial tension.
It sells newspapers.