You should be able to, but I think once someone else posts to your topic (if you are the first poster), you can no longer delete it. You can edit/delete your individual messages within a thread however.
SoundSpeed, the reasons for deleting are rarely due to "remotely off-topic" or "criticizing" posts. They have much more to do with the nature and tone of the poster.
'01 Spectra Blue
'94 Turbo Miata