Agree to an extent - some corporations can, some can't. Somewhat depends on what they produce and who they cater to. If their primary customer base is, say, hippies, they will do their best to maintain an environmentally friendly reputation. Another factor is who is running the company - I'm sure some companies are run by environmentalists.
However, privately run groups can be trusted, especially when their objective is to protect the environment. The Libertarian Party has in interesting article on free-market environmentalism here:
http://www.lp.org/lpnews/0411/libertarian-solution.html