There is a simple reason why such accounts shouldn't be deleted immediately when they're made: It'd enable this person to register with the same e-mail address again, and by that cause more work and trouble.

Now that (for example in the case of AEI) some time has passed, I don't see any reason to keep those accounts. On the other hand, I can't follow the argument of new visitors being repulsed. It's not as if the number of banned accounts is actually noticable. So in conclusion, yes, I have nothing against the deletion of accounts which had been banned without ever becoming active.