Why hope when you can just ask them to? Or ask them to actually mod the thread to a higher standard?
I guess I really fall on the side of rarely, if ever, deleting threads. Even as a mod, I don't want to delete threads because I feel they are common property of the board. If someone is breaking the rules, or the thread itself violates the rules, that's one thing. But a bad trade rumor that has two pages of responses already in a few minutes? That should never be deleted. It's the offseason. It's FULL of bad trade rumors. Who cares? If it's really a problem, the thread can be locked with an explanation. That way there's complete transparency.