I'm sure you're right. that's probably why Exxon and Monsanto are so popular with the environmental crowd.
But that's not what he said. He didn't say that sponsorship was to convince enviros. He said it's to convince those people that only need Monsanto's name next to WWF's to think, "well, maybe they're not that bad" (i.e. to influence the mildly concerned, not the enviros--minus the sell-outs of course).
Same thing with the fake "organic" labels: people who have a true understanding of healthy food will not buy into it, but plenty of people who merely have a doubt will.
WWF is also probably the least radical of all the orgs they could have sponsored, so they're certainly still minimizing costs (in this case, the benefits of sponsoring 'the enemy' outweigh the costs of doing so by giving these companies an air of environmental/social responsibility).