... the only reason to delete a node is if you realize it's a bad question, in which case it will probably already have negative votes by the time you try to delete it.

I think you're mistaken. "Bad" questions (like the one you posted earlier) are not considered bad by the community. They're fine questions. You were just embarrassed and wanted to salve your shame. Don't worry about such things. (Btw, I'm the one who restored the node's original content, putting it inside a spoiler section. Just so you know -- we do not like people to delete their node contents, and will restore them if we deem it appropriate.)

Truly bad nodes -- those deemed to be toxic to the site -- are easily taken care of by the normal consideration and reaping process.

You've already been pointed to How do I change/delete my post?; I hope you'll read it. And definitely check out the thread linked at the bottom, why a nodelet can be kept agains author wish?. It's entertaining as well as informative.

Thanks.