Most of modern society is (still) based on economic gain.
Many (most) people nowadays will find this logic, because they don't know anything else and society has worked like that for generations. Thus they think this is unalterable. As in former eras people thought it was unalterable that society were mainly based on war or on religion or on some feudal system or that the earth was flat. The same way that these ancient convictions turned out not to be necessarily true, it could turn out that economics does not necessarily have to be the base of society.