We pay taxes, and we spend money in America on American goods. I can only speak for myself, but the money I make doesn't leave the country (other than through huge corporations and their outsourcing :P).

The one thing we do not have though is a way to influence the political landscape of the country as we are not allowed to vote. So ultimately with a green-card there is taxation without representation, which I myself find quite ironic as the United States was founded on the principle that it was wrong to pay taxes and not be represented...