restrict users form sending friend requests (not members)

Restrict users form sending friend requests – restrict certain levels – not members

I think this would motive users to become members, because many users send a lot of friend requests and want to see the reactions from the other users, prior to become a member
and if they don´t get the desired reactions immediately they loose interest in the website.

The Theme has the option to restrict users form sending private messages right now,
but I think to restrict none members form sending friend requests would be a good idea.

Non-Members should only be able to view other profiles and nothing else.