Interesting... Taking @camo suggestion above, I created a role "new user" and it appeared in the registration tab. Removing the permission to sign in, removes the option from "require users to confirm their email addresses", however, if you keep the permission to sign in, and just remove the permission to add comments or create posts, you get the same anti-spam result.
Comments
Just for your info, there's a dedicated addon github too (for some plugins, some are in the "Garden" repo):
https://github.com/vanillaforums/Addons
https://github.com/vanillaforums/Addons/issues/26
Thanks for all the bug reports and help! We're working hard to make this our most stable release to date.
My 0.02