Agreed. Yes, consumers taking down Monsanto would be a rather large task, but that doesn't mean you can't do your best to support the other players (particularly those that might better fit your ethical framework). Money does very much talk in the U.S. (note how our political system works--donors and lobbyists)--it's just a matter of having enough of it (or, in the case of Monsanto, taking it away) to make a difference.
Not everyone has access to a CSA, and that's okay, too--you can still find ways to get at least some of your food that isn't a product of Big Ag.
I think it is also difficult to remember all the victories of "voting with your money" because so many have been normalised. Hormones in meat? Dolphin-killing tuna fishing? Formula better than breast advertising? There are myriad examples where a minority voted with their dollars and shifted corporate practice.
Are you old enough to remember supermarkets with no organic/free-range products? No recycled products? No vegetarian versions of products? These are all things commonly available now that have been introduced in my lifetime as a supermarket shopper.
Yes, it sure would be better if the consumer did not have to fight evil with every purchasing decision (it leads to decision fatigue, if nothing else). It would be better if representational democracy (especially in the US) worked better at looking after collective interests. But voting with your money? It does work, and I would be surprised if the Internet has not amplified its effect even further.
The cynic in me says, however, that much of the organic/free range food in supermarkets isn't what I consider organic/free range. Thanks to the lobbying of Big Ag, labeling claims for food don't necessarily match our own definitions.
That said, I'm not suggesting we stop--we just need to become better educated.
Not everyone has access to a CSA, and that's okay, too--you can still find ways to get at least some of your food that isn't a product of Big Ag.