Sure, I don't have a problem with people having children because of immediate benefits. That is when one should find whatever benefits you expect.
My objection is to the idea that people should have children so that we can turn them into de facto slaves when they become adults. There are many people on FR that view children as little more than future adults to suck taxes from or to serve them in their dotage. It is a pretty sick view, but a lot of people have it.
By your standard, every single responsible parent is a de facto slave. Unless you favor euthanasia for people when they become useless eaters, "giving back" to people who once gave is a reality.