This is, of course, the whole point, LB. Thirty plus years of identity politics has divided America up into various groups seeking their own self-interested goals, goals which can and do stand opposite that of other groups. A BBC video clip described America as being more like neighboring tribes now than back in...I think the example they used was from the mid-70s. The country is becoming increasingly polarized, increasingly oppositional, increasingly cynical.
Why? Because quite simply, people are easier to control that way. Whether it's through promises or threats, it's a lot easier to get people to go your way if you do this. Key one example - segregation. LBJ said after signing the CRA and VRA that the Democratic Party would lose the South for a generation (and probably more, now) when he did this. Why? Because the South were largely interested in only one thing - continuing segregation. What the political sphere has done today - on both sides - is divide people up with series of carrots and sticks, which it uses to either convince people to vote for them, or not to vote for the other guy.