Continue to ignore it all you want - but, there are plenty of examples of angry white people, who resort to terrorism to lash out and punish that which they feel is to blame for all that is wrong in their lives.
Just like Islamic Terrorists, who blame the west for whatever they feel is wrong in their countries, the white terrorists blame government and anyone not like them as the reason/cause of their problems.
White terrorists, right wing terrorists, American terrorists - whatever you want to call them; they exist and are clearly a valid threat (they are armed and willing to murder).