Alliance suggestion(or co-fed)

Well here is my idea that will never get implemented - why all those alliances aren`t made legal in a way, making people from allied feds unable to attack each other? I am sick and tired of seeing people from allied feds leaving the game giving out their stuff or simply feeding other empires. As our admins are intolerant to proceding against that in any legal way(suspension, blacklisting) because of "lack" of proof(how can you prove two feds are allied?), that would be a nice way to decrease cheating at least slightly.