A study by researchers at Stony Brook University took 111 undergraduates in political science courses and found that our political attitudes are shaped by people we interact with often.
From Pacific Standard:
"Our primary finding is that cohesive networks result in lower-quality thinking," they write. "Conversely, those who have occasional contact with, and loose attachment to, people with whom they talk about politics have richer and more causal thinking on energy policy."
"It seems that the feelings of strong attachment to one's network members are associated with those traits that underlie low-quality political thinking," they conclude.
At first glance, this seems fairly self-evident: If you regularly hang out with close friends who all share certain assumptions, it eventually becomes difficult to articulate the reasoning that led you to those common beliefs. But these findings suggest the problem goes deeper than that.
"Close-knit social networks generate low-quality reasoning regardless of the network's level of political sophistication, or the existence of a variety of political views in the network," the researchers write.