Since some sort of mass death is impending anyway, the government should just evaluate all genocidal and utopian programs objectively and dispassionately, and implement the best one. Here is my proposal:
After 2-3 generations, only rational actors will be left. Then the market will actually be efficient and we can have a libertarian or ancap utopia free of animal suboptimalities. When the only human motive left is the profit motive, all will be well.