Well, I could live with either taking the surplus from that specific program and investing it in the best possible way to cover for well-known coming shortfalls

Well, I could live with either taking the surplus from that specific program and investing it in the best possible way to cover for well-known coming shortfalls, or saying that it is a generic tax like any other tax. Then at least people would know where it stands. Instead we have a weird situation where the tax specifically calls out social security, but in reality gets spent on a bunch of unrelated things, with a thin veneer of technicality to make it all hold together.