I have a bunch of new users to add to the system and make members of the CanMys blog. When I added the first and logged in as him, I noticed that when I clicked on the Posts button, I was allowed to see posts from the Moses, EMCS and Scraps blogs. Turns out those three blogs had group permissions which made all users of type "Blogger" members and with permission to upload to the media folder, but do nothing else. Those three blogs also have individual users with specific permissions.
I disabled the is-member checkbox for Bloggers in the group permissions for each of those three blogs. That automatically disabled the upload checkbox. There should be no change of behaviour for specific users that are members of those blogs.