Why is it frowned upon to get a Hitler mustache?
Why is the "normal" populace of the United States shocked when one supports the Confederate flag?
& in the same manner, why does one look upon "white pride" as a negative thing?
You can say that you do not support what Hitler did, that the Confederate flag actually meant something else, or that "white pride" is just your way of conforming, but fact of the matter is that it is human nature to judge based off environment, culture, history, etc.
History lesson: Whites overtake India, whites bring slaves to America, whites invade the Moores, whites approve of slaves in America, white Americans view slaves as inhuman.
More recent history: White people bomb Japan, white people secretly provide weaponry for a coup/revolution in Colombia, white people don't allow certain races into the country, white people favor white people only, white people cause segregation, white people start KKK, white people white people white people.
"Why, sir, it's not like any of that is happening now."
Well you are ignorant if you assume that.
Sure the Egyptians enslaved others, but that was too long ago for it to leave an imprint on us. All of recent history has denoted the white race as negative in the sense of "racial supremacy". Because, as uneducated as it sounds, if you let white people express their pride in whiteness, they will become what they were not too long ago, or at least that is what other races would think.
Why were the Black Panthers/Muslim Brotherhood(african americans) not looked at as such a negative message?? Because they emerged as the "resolution" for the climactic end of the problem of race.
ALSO, please note, that white almost exclusively is the American white population in this case, as Europeans do have a disdain for white Americans, where as other countries have a hatred for white Americans.