No, you can THINK about anything, including genocide, or wishing everyone of the oppostite sex would disappear. I doubt anyone has much problem with various ethnicities which are generally considered "white" preserving their heritage, and thus simply indicating their respect (or "preference") for it. But there's a fine line between that and demonizing the "others", the crossing of which can lead, and obviously HAS led on all too many occasions, to attempts to exterminate that "other".
