You remember Pablum, don't you. The fine, soft cereal fed to babies. That is my impression of Patriocracy, a documentary that purportedly delves into why America's political divisions seem to be growing. It is a soothing explanation by the left, made to the left, to explain why the political right is so unreasonable.
To be forthright, I have not watched the whole documentary. After about 20 or 30 minutes, it was fairly obvious to see where the documentary was going, and that it had its sight on the so-called "religious right" and the "tea party."
The portion I watched was a series of snippets from interviews and short segments from news broadcasts to demonstrate that there is a greater political division (although no statistical or other empirical evidence was introduced), interspersed with comments from long-time political journalists lamenting how things used to be in Washington when politicians knew each other, and deep friendships could form across the aisle.
The documentary, up to that point, had advanced the hypothesis that Washington had become dysfunctional because politicians were being pulled away from the center by more vocal or radical elements of each party. Although the hypothesis was cast in a neutral manner, the documentary only displayed news clips relating to groups or people on the right, implying that this was a problem only with the Republicans. This was emphasized by stating that this split could be traced back to Sen. Goldwater's run for president, and Newt Gingrich's use of C-SPAN to directly reach the public--both Republican politicians. Nothing is mentioned about the 1968 Democratic Convention and the liberal left taking over the Democratic party, or the defection of many Democratic voters to the Republican party under Reagan. They didn't even use Reagan's famous quote that he did not leave the Democratic party, but the Democratic party left him.
Assuming for sake of argument that there is more political polarization now than in the past, I would offer some alternative causes:
First, as I noted above, the journalists (all of which I would consider to be liberal to very liberal) lamented how things used to be, before Newt Gingrich and CSPAN. What they actually are lamenting is the loss of a monopoly on the news. I would suggest that if there is more of a partisan divide now, it is partly the result of the ability to obtain news independent of the major networks and newspapers. Notwithstanding efforts to the contrary, people can now more closely follow what politicians are doing, and what bills are coming before the Congress.
Second, back in the "good ol' days," the federal government was less important in the day-to-day lives of Americans. If you were to look at the breadth and reach of federal law and federal agencies in 1970, it was much more limited. The federal government ruled with a lighter hand. Now, of course, it is much different, and so the average person has much more at stake when the federal government acts.
Third, contrary to the impression given by the documentary, I would suggest that the Democratic party has veered and lurched to the left of the general public on major issues. That is, it is not that the Republicans have grown more conservative (I daresay a middle of the road voter in 1970 would be considered very conservative now), but that Republicans have not moved to the left as rapidly as the Democrats have.
Fourth, I would suggest that what we are seeing is partly a result of increased tribalism within the United States, such as special issue voters, identity politics, antipathy between urban and rural voters, and so on. Because of modern communications, it is easier for members of a "tribe" to find each other and form political networks. The political networks that were traditionally the monopoly of the parties are being bypassed in favor of other networks.
Fifth, what were mild disagreements in the 1960's and '70's have become "cultural wars." Compromise is not an effective strategy because it became a one-way street only heading left. It is no compromise for one side to merely take less this time than they wanted, without giving up something else in return, and them come back a little later to ask for more. This is just letting the camel into the tent little by little. And many voters have come to realization to let just a little more of the camel in will result in their being kicked out of the tent.