Obviously you aren't going to be able to get everyone to agree on everything, but I think the vast majority of this is simply because people are easily manipulated, and are so prone to group think and jumping on the bandwagon. If it weren't for lobbying and political campaigns trying to tell you what to think, I believe that the vast majority of the public would be much more aligned.
Have you tried to get a group to consensus in an area where there isn't any lobbying or manipulation? People have lots of different ideas about how to do things, informed by different life experiences.
Political disagreement predates lobbying and campaigns by millennia.
