If by 'unchecked' you mean unmoderated, that's likely for the simple reason that we don't come close to seeing everything that gets posted here. You can help with that by flagging such comments or by emailing hn@ycombinator.com in egregious cases.
People breaking the rules doesn't make it ok for you or anyone else to break them, though. I replied to your comment because I happened to see it—it's not as if I recognized your username or have any idea what your views are!