Interest never lies. Karl Marx’s old rule of thumb is indispensable in judging the driving forces of individuals and groups. But if one takes a closer look, it is often more complicated.
There are at least three phenomena that mess up the picture for homo economicus. People can misunderstand their real interest, out of ignorance or under the influence of clever PR. People can define their interest in unexpectedly complicated ways. They sometimes have an altruistic side that neither Marx nor Darwin managed to explain.
All democratic politics revolves around these phenomena, mainly the first two. On the basic level, it is always about conflicting interests. The poor want resources reallocated, the rich want to be exempt from taxes. Organised interests, like trade unions or employers, by definition want to appropriate privileges at the cost of others.
On the next level, which is more interesting, it is about how people view the three phenomena abo...