Comparison is bad for you and also for society as a whole. More accurately, nations where the gap between rich and poor is the greatest are at more risk from all sorts of social problems.
It has been shown that people report the greatest levels of unhappiness in countries where the gap between rich and poor is greatest; the wider the gap, the greater the dissatisfaction.*
It seems that being poor is not what makes people unhappy, but living alongside people who are much richer than you does. There’s a a degree of tolerance and acceptance of different levels of wealth, but beyond a certain point that buffering effect disappears. I’ve simplified this, but it doesn’t seem to be in question that this is phenomenon is reliable and solid.
It’s not just societies that suffer, comparison is bad for individuals too. Findings by The Happiness Research Institute in Copenhagen show that when people are constantly reminded about others’ happiness they become unhappier themselves (why is it that we trust Scandinavian findings more than, say, Bosnian or Puerto Rican research?).
Researchers split a selection of Facebook users into two groups. One continued their lives as usual, the other went cold turkey and had no Facebook contact. After only a week the latter group reported that they were 55% less stressed and more satisfied with their lives.
Participants in the study were aged 16 to 76, and although the habits was difficult to break at first, the abstainers became significantly more satisfied with life, and were more focused and productive, and paradoxically LESS lonely than the other group.
I summary, comparison is bad for you because, at best, it leads to dissatisfaction and resentment, at worst, whole societies suffer on many different levels.