Very true. I am looking at it more from the perspective of taking power off the grid rather than putting it on. I use X amount of kwh per month. This energy must be generated by someone. In the current (default) configuration, the generation / line / distribution charges all go to my local company. If I opt for Green Mountain, my local company still bills me for everything (generation / line / distribution) but must pay the credits or pass on the generation amount to Green Mountain (at a slightly higher price), rather than to their own generation facilities.

The way I understand it, I pay a little bit more for power generation, but the money I pay is directed away from the local (almost) monopoly using coal / oil / gas / nuclear and directed to Green Mountain that (allegedly) uses hydroelectric and wind.