Except that you are wrong, I am from a big city, many of us are, Evangelicals live in big cities, lots of conservatives do, and it does not explain 150 years and more, of Jewish voting.
Care to explain the 1920 Jewish vote, or 1980, or why other groups that are not liberal can be big city people without voting liberal, or why some people seek to move to liberal centers, or away from them, or why Austin is so much more liberal than Houston?
According to you, people don’t have politics, they are just reacting to population density.
It's an oversimplification but in general that is how it works, not only throughout the world but throughout history. How many evangelical big cities didn't vote for Obama? Not the majority of them. Increasing density along with increasing libtardism is evidence of causation and not just coincidence. Yes, there are many exceptions with obvious reasons. Seeing the relationship though is useful for doing something about it. The 'crat leadership has been well aware of it for some time and have been doing everything they can to herd us into the big cities, going so far as to open the immigrant flood gates into the cities from third world countries.