Hmm, this doesn't track with history. Boycotts, and more generally collective economic action (strikes, etc), are an incredibly powerful form of protest. People have shaped the world through refusing to buy from oppressive forces - case in point, the boycotts of South Africa during apartheid successfully pressured South Africa out of apartheid. We got our collective rights as workers (40 hour work days, etc) through strikes, boycotts, and more.
It's not easy, but if you're serious about it is best done in community, with support and strategy. So, the opposite of main character syndrome, I would say.
It's also very odd that you take an analysis that is fundamentally systemic and translate it into purchasing from an individual psychopath - under what assumptions is that a valid comparison, one with any merit? It's not like corporations exist in a vacuum, only to emerge from the void to casually sell a single pen, the money with which they use to buy a single bullet. We as individuals, as communities, exist in feedback with the systems that we are a part of, including (surprise) corporations. So, yes, we have power to shape them, though (again) not easily.