[Erwin]

What I do is I create a new private forum, and call it "Trash". Then I remove all the admin options for delete thread.

I then created a button in the forumdisplay template that automatically MOVEs threads I want to delete into this private forum (or you can just manually move threads into this forum).

This way, threads are never removed, and you keep an archive of all bad threads for future reference.

Alternatively, there is a hack that you can use that preserves post count even after you delete threads.