I agree with you mainly--it seems nearly impossible to isolate any large agent in this interconnected economy--but you should remember that the main purpose of boycotts nowadays is to draw attention to the cause, both from the offending company and from the public. This can still be accomplished without following the dollars to every terminus. In fact, more focus on a particular product or set of products may serve to draw attention, at least in the case of the public, better than a broader campaign. Gandhi wasn't about to put the British occupiers out of business, and neither could he exist without interacting with them at some level, but he still made powerful statements by spinning his own cloth and making his own salt.
My opinion
