From The Federalist Papers, #10, by James Madison:

“As long as the reason of man continues fallible, and he is at liberty to exercise it, different opinions will be formed.”
“The latent causes of faction are thus sown in the nature of man; and we see them everywhere brought into different degrees of activity, according to the different circumstances of civil society. A zeal for different opinions concerning religion, concerning government and many other points, as well of speculation as of practice; an attachment to different leaders ambitiously contending for pre-eminence and power; or to persons of other descriptions whose fortunes have been interesting to the human passions, have in turn divided mankind into parties, inflamed them with mutual animosity, and rendered them much more disposed to vex and oppress each other, than to cooperate for their common good.”