Altruism - at least in biology - normally means taking an inclusive fitness hit for the sake of others - e.g. see the definition of Trivers (1971).

I thought it fairly obvious I was not using the biological definition of altruism. I was using the ethical definition of altruism - taking a self-interest hit for the sake of others' self interest. It's quite possible for something to increase your inclusive fitness while harming your self-interest, unplanned pregnancy, for instance.

Proposing that altruism benefits the donor just means that you aren't talking about genuine altruism at all, but "fake" altruism - i.e. genetic selfishness going a fancy name.

I wasn't proposing that altruism benefited the donor. I was proposing that it benefited the donor's genes. That doesn't mean that it is "fake altruism," however, because self interest and genetic interest are not the same thing. Self interest refers to the things a person cares about and wants to accomplish, i.e. happiness, pleasure, achievement, love, fun, it doesn't have anything to do with genes.

Essentially, what you have argued is:
1. Genuinely caring about other people might cause you to behave in ways that make your genes replicate more frequently. 2. Therefore, you don't really care about other people, you care about your genes.

If I understand your argument correctly it seems like you are committing some kind of reverse anthropomorphism. Instead of ascribing human goals and feelings to nonsentient objects, you are ascribing the metaphorical evolutionary "goals" of nonsentient objects (genes) to the human mind. That isn't right. Humans don't consciously or unconsciously directly act to increase our IGF, we simply engage in behaviors for their own sake that happened to increase our IGF in the ancestral environment.