After much frustration and little discussion, we've decided to add a new rule. Deleting the first post in a thread will now get you a warning. When somebody deletes the first post in a thread, it renders that thread useless, and any information that you guys have taken the effort to add to that thread almost always gets lost without context. This is easily as disruptive to the board as derailing a thread or making an unreadable post, so from here on out, it'll get the same treatment.
I know a lot of people delete their post because they think it'll delete the thread. It doesn't. So if you'd like a thread deleted, just ask one of the mods and we'll get rid of it for you.