Clarissa asks, "Is the expression white trash racist?"
I would say yes. Just like any other racial slur you can think of white trash is a term meant to insult, disrespect, or otherwise harm a people of a specific race. That's it. You don't call Latino people white trash do you? You don't call Japanese people white trash do you? No white trash is reserved for white people just like the racial slurs against Latino and Japanese people are reserved for Latino and Japanese people.
It doesn't matter how long the American Slave trade lasted or how many innocent people were killed.
It doesn't matter how long the Britain tried to colonize various other locations around the world through violent and underhanded means.
It doesn't matter how many people have donned the hood and cape of the KKK.
It doesn't matter how many people are in the Tea Party Movement or how wrong their views are.
And there is not enough white privilege on this plane of existence to justify using it.
Yes calling someone white trash is racist and it needs to be removed from our language just as much as any other racist slur you can think of.