Why are narcissists anti-social?
That depends on both the narcissist and what you mean by anti social. If you mean criminal behavior then it depends on the narcissist. There are plenty of narcissists that aren't antisocial.
If you mean asocial, once again its up to the individual narcissist. I'm sure there are narcissists that like people fine, it depends.
However for the ones that are, I suppose because they feel that since people aren't perfect then they're only worth contempt. But since I'm not a narcissist, I don't really know. You would have to ask the narcissistic quorans.
They don't have boundaries, they don't stop to reach their goal. Their goal is pursuit of narcissistic supply. People without boundaries are dangerous , they might not be anti social but usually can engage in such activities since no boundaries. Narcissist like society but for different reasons , narcissistic supply.