You want to give the opportunity to your community to express itself freely ? You wanna make your content available for a handful of people or yourself only? For all these cases, privatizing your website or blog may be useful.
This is not standard behavior for WordPress or BuddyPress. However, a solution exists. We recommend My Private Website if you wish to make you entire website private. Simply install and activate this plugin, and then go to the plugin settings page (Settings > Private Site) in order to adjust options according to your needs.
If you need more help, this tutorial seems to explain every steps in great details: