This is what they mean by 'game breaker'. It means you can't play using the same strats in our templates, you need to account for being able to be destroyed from within, which is for the most part undefendable. But yes, it's "fair" b/c it's a 'game breaker' equally for both sides.
This gives me the idea to make a mod that randomly kills people. There is an X% chance of a random player getting eliminated.
Might add a setting for custom dead message as well, so that you can get messages like "King {username} died of a heart attack" for diplo games.