Indeed you don't, but there's a lot the state can do to encourage and facilitate children being reared in stable families which can prepare them for an adult life which is a net benefit to their society.

Your cynical argument has value as well. The trouble is that the only even temporarily stable state thus produced is a single-party state, and you can't really kick everyone off the dole once you've finished using it to get where you want to go. It's an ongoing cost whose magnitude is only ever likely to grow over time, and the probable economic result is frightening.