I'm assuming we cant just throw the "excess" population into a volcano or something
Something similar was tried not so long ago and I doubt it will be the last attempt. I can think of quite a lot of people that will cheerfully sacrifice a mass of people on the altar of their basic ideology, and won't regard themselves as morally deficient for doing so.
Well, okay, lets just throw those people into a volcano.
(Is that an okay ideology? Or should you throw yourself into a volcano if you believe? I for one would gladly throw all the jerks in the world into a volcano and jump in myself afterward as I feel it would be worth it to be immortalized forever as the Last Asshole on Earth. Then you all could get on with your lives in peace and harmony. I expect life would be rather pleasant. I mean, can you even imagine it? A world with no assholes? Sure the four or five people left would be pretty lonely but at least there wouldn't be a littering anymore, eh?)
Something similar was tried not so long ago and I doubt it will be the last attempt. I can think of quite a lot of people that will cheerfully sacrifice a mass of people on the altar of their basic ideology, and won't regard themselves as morally deficient for doing so.