Statesboro, GA, USA
Desire is the impetus for all action. (With sub-questions--is inaction considered an action? And does that mean that there is no altruistic motivation for a good deed?)
Before we can answer that question, we should ask about the nature of desire itself. Is it always a form of selfishness, simply because it can't operate apart from the self? The way I see it, altruism would only be impossible if desire could never be other-directed and outwardly oriented, despite it's native ownership. I may own any number of things, which are nonetheless centered around the welfare of someone else. Desire, despite it's nativity, may still be a "foreigner" at heart.
Can you desire the good of another, for another's sake, for a true desire to see them better off? If so, then the fact that the desire resides in you (where else could it reside?) is incidental.
An author can write a book about a character other than himself. And we can't say that he is limited to writing autobiography, just because every word comes through his own mind.
I think what you are really asking is whether egoism is philosophically true. I think we've already had a couple of threads on that subject haven't we? I personally think egoism doesn't match some of our most basic assumptions about life. And I don't doubt those assumptions, as much as I doubt the philosophical pedantry of egoism, which seems to make some sense on the surface, but after some reflection shows itself to be another over-simplification.