Most of the time my in-group consists of just one person: me. This group is too small to generate the feeling of belonging that I and most people seek.
On the positive side of in-group thinking you get to overcome the feeling of isolation and loneliness that sometimes assails people. On the negative side you tend to lose empathy for those outside your in-group and exaggerate the difference in virtue between them and you.
It would be good if everyone belonged to your in-group so there would be no one to despise or be suspicious of. Even so, I still see one or two hitches in this. The first is that we sometimes dislike even those in our in-group so our negative feelings are unlikely to wither away completely. Some of us even dislike our own family and you don’t get much more in-group than that.
Secondly, humans find it hard not to think in terms of ‘them and us’ and fighting this natural tendency requires some effort. I’m not sure I can be bothered, especially when social scientists tell us that some of the most unselfish human actions are performed only in the context of in-group solidarity.
The third problem is philosophical rather than psychological-sociological. The nice feeling we get from belonging to a group requires the existence of an out-group, just as the pleasure we get from music presupposes the existence of silence or random noise.
Even if it does prove possible to eradicate in-group-out-group-thinking, I wonder what kind of person would be able to think that way. I picture him being able to sympathise with every point of view, thus making it impossible for him to take sides – even his own. How this person would be able to make decisions and act is a mystery to me, and whether he constitutes an improvement on normal human beings with their preferences and biases, I find it hard to say.