One must add at least the minimum words. I usually use something like "Content to prepare for deletion"
One must also have a title and a selected primary tag. Doesn't much matter what either one is as long as they meet the requirements.
Then you can delete the blog.
As far as creating empty blogs, when you are editing one blog, you can also create a new one from the side menu. I suspect there is an autosave function that does not care one way or the other about the validity of the content. Once you have created it, without any other content or input, you then have to go through meeting the minimum blog requirements before you can delete it.
IT should probably review this and move the minimum requirements to the creation function instead of the deletion function.
Regards, Mike Appleby