[A] piece of religion in this country for a lot of people is a basic kind of ethnic tribalism. Most people aren't genuinely very religious and most of those who profess to be don't have any kind of sophisticated understanding of what their religion is supposed to be. They do know what team they play for, and that's important.
Right. See this local example from a few years ago:
Mrs. Dobrich said she had asked the board to develop policies that would leave no one feeling excluded because of faith. People booed and rattled signs that read "Jesus Saves," she recalled. Her son had written a short statement, but he felt so intimidated that his sister read it for him. In his statement, Alex, who was 11 then, said: "I feel bad when kids in my class call me 'Jew boy.' I do not want to move away from the house I have lived in forever."
Later, another speaker turned to Mrs. Dobrich and said, according to several witnesses, "If you want people to stop calling him ‘Jew boy,’ you tell him to give his heart to Jesus."
Humans are social animals, but belonging to a tribe - otherwise known as being in a gang - is a basic unit of "society". It requires a higher level of abstract reasoning to consider yourself a member of a group that primarily includes people you don't know and who may look and behave in ways very different from you.
Nationalism is a common way of conjuring this higher level of belonginess. In America, nationalism was made possible by the exclusion of blacks from the definition of "American." Once that notion was undermined, whites started either turning away from nationalism or re-defined "the nation" using their own idiosyncratic measures. The rise of the Christian gang as a political force in America is the result of both of these reactions. On one hand, white conservatives have to some extent become Christians first and Americans second. On the other, Christians have conflated Americanism and Christianity, and thereby imported the requirements of the bigoted form of the first - xenophobia, militarism, exceptionalism - into the second. To conservatives, they are the nation, and anyone who is "other" must be silent or be driven out.