alt Hacker NewsI don't think this is necessarily the assumption. The US labor force is less than 170 million [1], so less than half of society is in the labor force, and that includes unemployed. The total labor force participation rate (so we exclude institutionalized peoples, children, etc) is about 60%.
And while there's plenty of push about lowering unemployment and so on, I don't think the concept of getting more people into the labor force, or back into it, is pushed by any group at all. On the contrary the push for immigration is largely shrugging our shoulders at the fact half of society isn't in the labor force.
Of course if somebody isn't in the labor force they still need to find some means to provide for themselves, but I think that's quite different than the assumption everybody should be working.