1. I understand the confusion there. To hide the buttons in the registration view if the setting is disabled, you can use the following workaround (which I'll check in the change).
In /plugins/system/jfbcsystem/jfbcsystem.php around line 138, replace
if (JFBCFactory::easytags()->canExtendJoomlaForm('registration', false, $showLoginWithJoomla))
with
if (JFBCFactory::config()->get('social_registration') != 0 && JFBCFactory::easytags()->canExtendJoomlaForm('registration', false, $showLoginWithJoomla))
2. We can't just use the setting from SCLogin for the JFBConnect component, as not all users also use the SCLogin module. I'll have to think about how to best update the styling when the component adds the buttons (like with easy-tags or the login/registration views), whether a new setting or moving some settings up to the component. In the meantime, it sounds like you have temporarily added a style to your page. I'll adding an issue to the tracker to address this.
-Melissa