I am suggesting adding the option under Organization > Settings > Home Page to allow administrators to disable the Gallery and Groups navigation/menu item for non-authenticated users when the Security setting of "Allow Anonymous Users" is enabled for the Org site.
When Allow Anonymous Users is enabled this entitles anonymous users to see the Home page, Gallery, Map, Scene and Groups making them visible without authenticating. Anonymous users would be able to access the map, add content to the map (public layers) to explore data but wouldn't be able to save them or share them.
By disabling these links, and only making them available to authenticated users, this will allow the Home page to still operate as a landing page or splash page without providing the public a method to discover public items easily. Other options currently exist such as Open Data for public users to browse org content.
Also, to allow Hub community members to create an account through the sign-in dialogue ("Create a Community Account"), the Allow Anonymous Users setting must be enabled for the Home/Employee Org thus opening the Orgs home page, Gallery, and Groups for public browsing. For Orgs that prefer a more secure site but also want to enable Hub there is no choice to enable Hub but to also retain some level of control over sharing the Gallery and Groups.
Orgs should have the choice to disable these navigation links which can provide the org more flexibility in terms of managing users and content.