Voting with your wallet is literally plutocracy -- those with more dollars get more votes.
Not only is our theoretically bad, but it's practically bad: the impact of a boycott is negligible, but the impact on the people doing the boycott is huge: not having access to the conveniences everyone else has puts us at a significant disadvantage compared to our peers.
And finally, it's not just practically bad, it's actually contraindicated. The executives of a corporation are legally required to maximize immediate returns to their investors. It's literally illegal for a CEO to move a company in the direction of civic responsibility over profit. And it's not just "profit" -- it has to be increasing profit. Line has to go up; they can't just keep it flat, even if "flat" is hugely profitable. To withdraw our financial support will just cause them to squeeze harder on everyone else.
(There's an argument that there might be more profit in social responsibility, but unless you have numbers to back that up, and it demonstrates immediate returns in addition to long term benefits, then it's just a guess, and a guess is never going to be more convincing to shareholders than facts.)
The only way to change this is with regulation, and a cultural shift away from "line goes up" mentality. And you can't effect political change when you're spend 3x as long making dinner because you're boycotting processed food.
Suggesting that we just give up all the conveniences that our labor, our creativity, and our cultural contributions have enabled, for the sake of convincing a CEO to be nicer is just ineffectual.