The line of thought that Kurt Vonnegut describes on p. 27 of Breakfast of Champions isn’t true of all people, but it is still distressingly common.
Ideas on Earth were badges of friendship or enmity. Their content did not matter. Friends agreed with friends, in order to express friendliness. Enemies disagreed with enemies, in order to express enmity.
There is a good reason why Vonnegut’s depressing observation is true. Humans evolved as a tribal species, and we haven’t quite grown out of it yet. This is one reason an immigration debate still exists, even though economists decided the issue more than two centuries ago. More to the point, agreeing or disagreeing with people for merit-unrelated reasons is one way that people define their in-groups and out-groups.