The U.S.A., for example, has 300,000,000 residents, but yet there is still numerous areas of land with little or no residents. Ditto for Canada, Russia, and some parts of Asia and Africa. A lot of people inhabit metropolitan areas and coastal areas, thus resulting in a high density figure. As a generalization, if people were better distributed geographically, a "wildly overpopulated world" would not be your statement.
Ed: It's this argument that "there's still land to live on" that makes me want to strangle idiots like Rush Limbaugh and his Republican cronies. Sure we could cram every person on earth onto the island of Zanzibar, if we all stood nose to nose. The POINT about population problems, is that the world contains lots of places where it's next to impossible to live, places that lack fertile soil and drinkable water, or enough water for crops to grow. And much of the earth consists of deserts and mountainsides and flood plains, and tornoado alleys, and fault lines, and dry scrublands and canyons and jungles where it's difficult to live, to say the least. (Not to mention that "spreading people out more" also leaves a food "distribution" problem, and health care distribution problem, etc.)
As for water, PARADE magazine had a front page article asking whether or not we would have enough in the coming decades for everybody on earth. Ground water pollution levels continue to rise, and areas of America and the world already are experiencing droughts and water shortages. My own town can't even process all the sewage and we've had contiminants in our water supply for decades now, sometimes people DIE just from drinking it. Not to mention that with industrialization came a huge increase in the needs and uses of water in general. Then there's the garbage factor and the recycling factor. Even at the present level of population, our low level of recycling and adding new pollutants will eventually kill mankind, we have to reduce those levels, and one way would be to simply reduce the population.