Individuals can do little

It has to start somewhere even with baby steps. Otherwise nothing will be started at all.

Going after corporations - I am afraid to say - is "barking up the wrong tree.

I do not think so. It may not be enough because they are not the only ones responsible in the totally of the issue but again, something has to start somewhere. For Greenpeace specifically, they do not receive donation from corporations and government bodies to keep the impartiality because they can protest against any of those corporations and government.