Click on the time of the comment (right after the poster's name). On the new window, click on the "flag" link. I think that calls it to dang's attention.
And yes, dang responds to this kind of garbage, no matter which side it's aimed at...
The comments that I saw you responding to did not seem to be very directly about race. You want us to exclude someone from here because of their statements elsewhere. We don't agree; feel free to leave in righteous indignation if you so choose.
When I see a comment advocating for actual white supremacy, I will flag it, downvote it, and do my best to rebut it. If you see that as "welcoming", so be it.
If you're concerned about abuse on HN, the thing to do is email hn@ycombinator.com, not take threads off topic like you did in this thread. We don't see everything on the site, and can't act on what we don't see.