First, make the distinction between the common usage of "altruism" and "ethical altruism". Ethical altruism is essentially the doctrine that we exist for the sake of others. Comte coined the term and wrote:
The crucial point here is that justifying actions that benefit others on the basis that this will in turn benefit you is not proper in the context of ethical altruism. According to ethical altruism, you are obligated to serve others regardless. An argument that you ought to act in a way that benefits society for the reason that you will receive long term benefit is an inherently egoistic argument, not altruistic.
Second, keep this Rand quote handy: