Historically speaking why are ulstermen so racist?

British have been very important in the world of scientific racism, therefore if you are a british nationalist you also must be somewhat pro racism.
I would rather ask why are irish nationalist more empathic with other races.
This is because the irish have always been opressed by the brits, the same oppresion happened in their colonial possesions therefore I think its like unity within the oppresed.
An example of this is when our irish brothers helped us mexicans in the mexican american war.