Just as we can assume that the fact that the consumer bought the product means that there was a good reason for buying the product, the fact that some people would choose to boycott the store means that they have weighed the pros and cons and have decided that a boycott is more utile than inutile.
I'm familiar with this argument. Indeed, I vaguely remember making it myself, in a discussion with you many years ago, around the apex of my libertarian period. Nevertheless, it's a bad argument. The analogy fails because buyers don't choose products because they're good
. They choose products because they're good for themselves
, ignoring the impact of their choice on third parties.
This distortion will not matter much if consumers choose among produce and their choice impacts themselves far more than third parties. But that's not true for their choice to boycott in the name of ethics. What's good
about the boycott is mostly driven by impact on third parties. Yet what's good for the boycotteer
--- like the pleasant feelng of moral superiority --- is still what drives their decision. Boycotteers get this feeling no matter if they carefully weigh the consequences for others. Indeed, at least in my experience, they will more likely detest than welcome suggested improvements to their analysis. Hence, while the theory of rational consumer choice does predict sound(ish) choices about consumer goods, it predicts bad
choices about things like boycotts. The reason is market failure due to externalties.