I does far more good to write the company and let them know that as a PAST buyer of their products, you won't be buying anything from them again, and then let them know why!
Do NOT underestimate the value of a good letter and the impact it will have...or perceived by the seller of goods. Nearly all companies are feeling the pinch because of the economy, and if they feel that their position on anything controversial is costing them business, they will likely recant...at least publicly, and that can be a positive thing for the cause you are working for.
Never underestimate the power of the buck.