How is xenophobia part of having a responsible and informed dialogue. He dug through, found out the person is a different nationality and is not American. Then assumed they are not informed enough (in the best case) to make a valid argument. Which turned out to be wrong because they actually lived and worked in the area and other parts of the US.

I failed to see how this was an informed and responsible dialogue. I think we might have a different perception of those terms.