Take your pick: medical care, food production, forest reserves, farmland, fossil fuels, automobile traffic, military conflict, education, air travel, water, fish population or good old quality of life. Greater populations stress just about everything.
There are the Panglossian dreams that more workers will produce more taxes for more government services, but the demand for services will always outsrip the supply of revenue.
The same applies to everything else. The more a human being has, the more they want. As there is no infinite resource, by logic there is a cap and a diminishing curve of supply of just about everything. At some point the demand curve will always rise above the supply curve.
