I don't really have that much faith in the political process, I guess. It takes massive amounts of donor money to run a successful campaign, and we've all seen how often it happens that a representative gets to Washington and accomplishes exactly nothing that he campaigned on. It takes far fewer people to cause a change in market preferences than it does to elect enough legislators to build the momentum for changes to the law, and shopping choices aren't complicated by the myriad other issues involved in deciding who to vote for.
Just look at what has happened recently with high fructose corn syrup - not that long ago it was in everything. Organic was the only choice for HFCS-free bread, yogurt, ketchup, crackers, etc. But now Wheat Thins, Gatorade, Heinz, Aunt Millies, Pepsi's "throwback" line, and many other major name brand products have phased it out, all in response to a small but vocal and growing minority of consumers.