It's an investment that the parents will reap 10000x the benefit compared to everyone else in the society.

Also, it's very rare that people think they are going to bear a child to improve society. Adoption would make much much more sense if that was their goal.

In any case, people want to have children, sure.

Then they complain that having a child is so tough so much hardship (e.g. no vacation ever in this thread, child tax credit is not enough). Then, they turn to society to support them in an unfair way

Almost everyone knows the estimated cost and effort upfront. There are tons of materials and prior experience.

It's like me spending all my cash on Tesla and then complain that society doesnt support me enough.