The bar is higher than "interesting enough to garner upvotes".
Here's what moderator 'dang said about this issue a few weeks back:
Some of you feel that such stories are so important that the flamewars around them should just be allowed to burn. Our experience and observation suggest the contrary: they are bad—existentially bad—for the site. Like fire in general, they lead to more of the same. So the alternative to the current policy is conflagration. The best aspects of HN, in our view, would not survive this.
