1. More hands is not always better.... more hands means also more mouths.... more resource needs... less personal space.. less land.... more polution... lower quality of life... it aint sustainable

2. You got a point about GDP.... but if GDP growth at the expense of inflation.. it is not a real growth.. it is just growth in the value of products and services.... and finally the important part is purchasing power of consumers... and that does not improve simeply with GDP growth.. it improves with GDP growth and low inflation

Of course it is not a simple math... there are many factors and variables... but the overall trend and relationship are valid