If we give money to open source lobbyists then they can do the work of influencing the government so that bullies like the RIAA are a thing of the past. It also means that free software gets some legitimate representation, and by proxy the people who contribute to free software either casually or professionally are largely better for it. There's also some merit to the idea that free software cannot depend on corporations and although good will has prevailed here, far too often it hasn't.