I don't know the answer to the question as I know next to nothing when it comes to visas, but I believe I understand the question. I think etops777 missed the point – here's a scenario – imagine you are a citizen of Patagonia, or worse still, Nomanslandia. You have a green card so that's great – you can live and work in the USA and you can come and go as you please. But you want to go to Mexico? Well, you need a visa. Going to Canada? Visa required too. Going to Brazil? Sorry, you need a visa. Any country you want to go to – you need a visa because you are from an unpopular country. Now how inconvenient can that be?
Yeah you're right I forgot that some countries require visa's to get in other countries. I did miss the point. :o
