That's pretty loaded language, but it makes sense.
When an area is sparsely populated it doesn't matter as much how people behave. They aren't harming other people because there are none around.
As the population density increases the same actions like emitting pollution of one kind or another (air, sound, light, etc...) becomes a problem and all of the other people come together to ask you to stop, thus infringing on your liberties.
All of society is just people trying to get along with your neighbors. The more people you live near with the harder it is to stay on good relations with all of them. As the population continues to grow it becomes increasingly difficult to not live near other people, effectively impossible for an ever growing percentage of the population.
Some of this may even partially explain the rural/urban divide in politics.