I don't think this is a reason not to use them but... right now no one cares about those indices - but as soon as they're between corporations and their profits then there will be a whole lot of lobbying and you'll likely see an index review committee headed up by Reginald Thomas III (son of Reginald Thomas II - CEO of Megacorp X) suddenly insert themselves into the official publication of those indices - then the quality and neutrality of them will drop.

Everyone is fine with you saying "Don't cut down the rain forest" until you actually stop people from cutting down the rain forest.