One reason I find the delete, or edit useful is, sometimes I'll type up a comment come back a while later, read it, hit post without really thinking, and then go back and see the context, and realize I'm an idiot[0] and quickly edit or delete the comment before anyone else finds out.
It seems like you are saying that the utility of the delete function is that it allows a user (you, me and everyone else) to submit comments without thinking about the content and quality of the comment. What is wrong with increasing the incentive to do a "am I being a moron check" before hitting submit?
[0] http://xkcd.com/481/