Looking back to the time the United States decided to invade Iraq we seemed to come together as a nation. France, Germany, and Russia pleaded with us to not do it. We, as a result, stopped eating at French restaurants and started calling French fries American fries. Most of us will now agree that that invasion of Iraq was an expensive mistake.
If we are Red Sox fans we dislike anything Yankees, same with Dodgers and Giants. We either like Fords or we like Chevys. We don’t need facts to make these decisions.
It seems that it is human instinct to become emotionally attached and we don’t need reasons to do so, we will make those up as we go or accept what we hear that is in line with our emotionally based decisions. This causes us to be susceptible to group think.