Instead of focusing on the toilet itself (whatever type one might use), I would focus more on overall sanitation systems and clean water. Yes, it is true that a billion people (more actually) do not have access to clean water or safe disposal of human waste. From my standpoint, this honestly is a huge deal -- clean water and proper sanitation would most likely improve health in many areas of the world tremendously.
(In a way, this does tie in with the micro-organism disease theory mentioned by another poster above. When it comes to "most important ideas in human history", in terms of human lives saved, this has to be one of the top ones.)
(In a way, this does tie in with the micro-organism disease theory mentioned by another poster above. When it comes to "most important ideas in human history", in terms of human lives saved, this has to be one of the top ones.)