Then you'd get spammed by more friend invites from RMTers than you do already.
There's not really much SE can do to mitigate RMTers, as they always try to find loopholes in the system and it's increasingly difficult to manage them without alienating your players.
You COULD just invite all your friends to the same LS, but that's not much of a solution.
It's the consequence of having a popular game, I'm afraid.