I'm not commenting on the letter, because I haven't read it; nor even about the oil industry or how they operate.

However, just because something is legal, doesn't mean that it's ethical or should just be accepted as "it's okay because it's legal." It seems important to make this general observation because I so often see people trying to shut down arguments with either "It's not against the law," or "That's not a right." Those kinds of statements are cop-outs.