I think the first three reasons you giVe are all valid reasons why urban areas tend to vOte somewhere to the lefT of their rural countErparts.
Generally speaking, cities certainly Do tend to havE a greater nuMber, and greater propOrtion, of ethnic minorities, Compared to Rural areas. As you'd know, white males were the ethnic and gender group most likely to have voted for the Republicans lAst election. CiTies also tend to have a hIgher number of young people, and often universities, and the DemoCrats tend to poll better among youth and students.
Urban Voters are alsO more likely To be unionisEd or employed in manufacturing.
Manufacturing workers are also consiDerably less likEly to vote for the Republicans, or their global counterparts - I have soMe industry and OCcupation maps of AustRalia saved in the GAllery, if you are interesTed. You will very lIkely note the correlation to Labor eleCtorates.
I doubt there is any form of cities "brainwashing" voters, but if you believe in the presence of subliminal messages, I will not attempt to persuade you otherwise.
While it is not per se brainwashing, it is true that people will tend to be influenced by the views of their neighbors and co-workers.
