It's a narcissism of colossal proportions. We're all afflicted with this form of blindness in one degree or another. We see it in everyday life and we see it in our politics. We all tend to justify doing something that is in our own interest by suggesting it is good for all. Managers equate their own success with what is good for their employees.
Politicians invariably believe their own reelection is nirvana for the electorate.
So much of our politics is based solely on self-interest. But I suspect things are changing a bit. I'm not suggesting we've all become altruistic, but here are two examples. What this suggests is that people, for better of for worse, are not choosing party affiliation purely on the basis of their own economic benefit. In fact, they are often voting against their economic interests.