I think what the author was trying to get at with 'some people believe' is that most of the 'reasons' people fall back on to support their positions are in fact

I think what the author was trying to get at with 'some people believe' is that most of the 'reasons' people fall back on to support their positions are in fact simply personal opinions. Or opinions reinforced by there social group or social media 'friends'. Extreme polarisation is one of the results of segregation. The media and now academia with 'safe spaces' are pandering to segregationist impulses. People who are never challenged with opinions that they disagree with are much more likely to believe there opinions are facts. Or even that they simply they do not need to even consider opinions that disagree with there own and never develop the social skills to constructive deal with a diverse world of ideas and opinions.