I think Earth Day is great - I teach my students every year how to be good stewards of the Earth. I always read The Lorax and we discuss what the Once-ler could've done so that the Truffala trees didn't disappear. We talk about how it's okay to cut down trees to make things we need (furniture, paper, etc.), but it's important to not strip the land and leave it barren and ugly.
Extreme environmentalism (like Gore's documentary) cater to the crazy environmentalists who think that using electricity and hydrocarbon vehicles will eventually destroy the Earth. Judging by the lack of people who are participating in Earth Hour tonight, most agree that it's absurd.