A page can be so hopelessly irreparable that the only solution is to blow it up and start over.
Copyright violations are traditionally blown up, and anyone can start over as long as their version isn't itself a copyright violation.
Sometimes, the damage is beyond fixing. While you can edit any page to fix the page content, you can't edit the associations and social history of a page, even if you delete every trace of that page on the wiki. Most often, this is common with perennial policy proposals that have been the subject of so much fighting that even a brilliant, earthshattering work of genius would face significant opposition just because it's proposal #3941. And no, your version probably isn't a brilliant, earthshattering work of genius. Your best bet under these circumstances is to let the fight go and let the perennial warriors blow each other up (or at least wear each other out) and try again later, if at all.
Sometimes, the damage is fixable, but the effort in doing so dwarfs the effort involved in merely starting over.
With articles, this is the TNT tipping point argument: if the article's content is useless (including all the versions in history) but the title might be useful, then delete the content to help encourage a new article. If you keep the article, then you're keeping something of no value until someone replaces it with something of value, when people tend to be more inclined to fill red links. When you see this as an argument to delete, don't give up. If you can repair the article in a timely manner, then you've neatly refuted that the article is irreparable. If you can't repair it in a timely manner, then this is the simplest argument to refute at WP:DRV; after all, they said it couldn't be fixed and you fixed it.