Zinn presents the idea of the "permanent adversarial culture" in Chapter 22. There, he says that there is a group of people who will not accept the ideas that mainstream Americans of both parties hold. Zinn says that there were millions and probably tens of millions of Americans who would not go along with the status quo
which set limits on American reform, making sure that capitalism was in place, that national military strength was maintained, that wealth and power remained in the hands of a few...
The free exchange of knowledge that we enjoy in the US (particularly since the explosion of the internet and of social media) helps to keep this group of permanent dissenters alive. In the past, their actions and beliefs were not much reported by the media. Today, there is much less need for the media to report their actions because they can publicize themselves on the internet or via Twitter. The internet has allowed dissenters to find out about one another and connect to one another, thus making it easier to maintain the "permanent adversarial culture" Zinn speaks of.