Such a small proportion of people who visit news sites vote that a group of zealots can easily overtake a site like this. Spammers are comparatively easy to guard against; they don't care enough to create 100 sockpuppet accounts, and in any case the guys at reddit wouldn't have any qualms about killing spams that seemed to be merely for profit. This is a tougher problem.
You could say all the anti-C++ stories were already evidence of this problem. But a large proportion of programmers, even C++ users, disapprove of C++, and an even larger proportion of the kind of people who would use a social news site.
The Lisp zealots are another matter. This is more like spam; it's not just people who hate C++ so much that they reflexively upvote stories that sound critical of him; it's a deliberate attempt to market something online.
Incidentally, I'm not saying this because I have some kind of ulterior motives. I think C++ is the worst language of my lifetime. And I am not anti-Paul Graham. I know nothing about him except that every article he writes makes it onto reddit--no one writes that much gold.