Overpopulation is definitely a huge issue, but one that is largely ignored by the majority of people since it takes a great deal of care to approach it effectively.
Thomas Robert Malthus raised concerns about overpopulation in the late 18th century, proposing a theory that humans have a tendency to always overpopulate a given area, thus famines are unavoidable. The theory is largely dismissed today given that agricultural improvements have enabled us to increase the population by several times since then, with less famine than ever. However, I would argue that it is simply taking longer to come to fruition, not to mention the fact that human population growth has come directly at the cost of a mass extinction event (the Holocene extinction).
From the '50s,
John B. Calhoun proposed a newer theory called the
Behavioural Sink, demonstrating a link between antisocial behaviour and overcrowding via experiments on rats. As someone who is a professional driver, I can attest that human behaviour ranges from waving politely at strangers in remote rural areas to feral narcissism in the big city peak hour.
One challenge in dealing with overpopulation is that the same people who support anti-natalist views are the same ones who actually care about issues of consumption, ecology and ethics. Others (including the highly uneducated, religious zealots, drug addicts) do not give a damn and will breed freely. This in turn breeds out thoughtful and caring people and lowers the standard of human behaviour further.
The second issue is that the nature of questions of overpopulation reduces humans to mere numbers, and can easily give rise to racism, 'eugenics', support of mass murder and other dangerous philosophies. It attracts extremists like moth to a flame and causes more balanced people to avoid the topic outright.
I don't have the answers, just adding some food for thought.