You don't directly know what the poster has gone through. Prefacing the statement with "as a white male" implies that you know what the poster has gone through because of his race. It is willfully blind. You can make convincing statements that white people in general in certain states at certain times face certain kinds of systemic discrimination. You cannot truthfully make the statement that the poster has not encountered serious discrimination, malice, or personal difficulties merely by knowing his race and sex.

>presumably hasn't experienced that, or they'd immediately understand

This is a Scotsman fallacy. I am certain I could find some people who have faced terrible racism that would agree with the poster's opinion.