In the end, everyone is motivated by self-interest. Even if you're sacrificing yourself, you're identifying with something as an extension of yourself.
The ability to identify with something outside the traditional bounds of self depends partly on empathy, a facility or skill that is not equally distributed in the population.
To see someone's self-interest in their actions, in other words, is not, or should not be, to invalidate that person's actions or words.
In the end, everything we do reduces to some form of self-interest. Proving it is so for someone should not be demeaning. It is always so.
What we should instead critique is how and with what effect.
