Because there are racial-alike tensions within the Caucasian people, such as Nazi/Jews, West/Slavic, Protestant/Catholic.
It's amusing that bringing up facts in a community ostensibly self-selected to prize discovery and reason is sufficient cause to be silenced.
pg and the community he fostered has come a long way since this: http://www.paulgraham.com/say.html
Edit: would just like to point out that I was flagkilled before any response came, so currently my post is invisible in this thread.