Population Growth Is Directly Proportional to Assholery
There is a clip that shows a small child being run over by a car. The event takes place in China. Passengers pass by and nobody even attempts to help. I am not going to post the video. Do the google search yourself. There are plenty of such examples in densely populated areas.
I grew up in a small village where everyone knew everyone else. Whenever someone needed help, somebody was there to offer assistance. Whenever someone fucked up, the individual ended up being stigmatized from the entire community. When I moved abroad, eventually ending up in New York, I witnessed the exact opposite. People in need where exponentially more but people rarely attempted to help. Good Samaritans were so rare that some good acts were going viral on youtube. Most people apparently were in awe since witnessing a heroic behavior was rather a rare phenomenon that they had to share. I am sure you have stumbled upon these videos as well.
Behavioral ethologist John B. Calhoun coined the term "behavioral sink" to describe the correlation between population density and societal collapse. Various experiments were performed such as in populations of cats and rats and similar patterns were observed. As density of populations increases, violence and mortality also increases leading eventually to a total population collapse. You can watch the rat experiment below.
"...But... We Are Not Rats"
Steven Pinker argues that violence has decreased. I beg to differ since he bases his argument on gross generalizations and a rather poor definition of violence. Many people seem to site his books as evidence but on careful examination all his claims almost can be debunked. For example he takes into account mostly major wars that are outliers of human behavior and he counts only deaths. If one takes a closer look into the facts they would realize that major wars have decreased but mini-conflicts have become a daily basis. For example USA has been having open war fronts for the last 50 years now. Countries have also realized that war can be fought much smarter such as by economically isolating a country. It becomes harder and harder to actually count bodies this way. Moreover, there is absolutely no evidence that early human societies were violent. In fact, the opposite has been demonstrated to be true.
Small societies tend to agree upon a common code of behavior. This is also observable in families and friends. The reason there is more trust is because people engage with each other more thus developing more intimate and trusting relationships. As population grows, competition and alienation also increases. Various events can happen and action-causative events between members is hard to distinguish. As a result, people become more vigilant and devious in an attempt to protect themselves. Moreover, disease spreads much faster and infections that could be otherwise be controlled mutate on a different level, having a devastating effect.
The economic model upon which humanity operates right now is location and resource depended — hence why we observe so many people in major cities. The U.N estimates that 54% of the world’s population lives in urban areas, a proportion that is expected to increase to 66% by 2050. Currently, we are on the fringe of creating superbugs, aka bacteria that are resistant for modern antibiotics. If we continue with this rate without changing the way we live, then we might see a massive correction in our population "bubble".