Thanks for your thoughts martey.
The reddit comment thread you are linking is indeed a bit old. Here is a more recent, really good discussion: http://www.reddit.com/r/TheoryOfReddit/comments/1ao3zf/shoul...
(as an aside: I didn't mean to by too coy about what my extension was or that I'm talking about reddit, I just wasn't sure about the etiquette of trying to publicize something by name here)
As for your points I have to disagree with both of them.
1. No users are ill served my extension. Somebody who posts something to the internet in a public forum and expect that they can delete that information whenever they want are ill-served by a system that perpetuates such an illusion. This often manifests itself as the Barbra Streisand effect.
2. My extension does not increase load on their servers. It does not interact with reddit servers in anyway. I can see why the old thread would lead you to believe that, but it is no longer the case.
I understand this idea is somewhat controversial but it is not immoral or unethical, just different.