To me the white poppy has overtones of the white feathers which were presented to young men not in uniform during WW1. I know there is absolutely no connection - quite the opposite intention in fact - but there is disapproval echoing from them - as though those who wear a red poppy were thirsting for blood and violence, not mourning the victims of that violence.
In some cultures, white is the colour of death. I could understand it if in those countries they used a white flower, but not here - Flanders fields were filled with red poppies, not white, after the destruction and disturbance of trench warfare.
"In Flanders fields the poppies blow
Between the crosses, row on row,
That mark our place; and in the sky
The larks, still bravely singing, fly
Scarce heard amid the guns below.
We are the Dead. Short days ago
We lived, felt dawn, saw sunset glow,
Loved and were loved, and now we lie
In Flanders fields."