I think GP was downvoted because he criticized consumer activism and not just what he meant to criticize: Making change by purchasing decisions. I've generally switched to his perspective. For about a decade I felt (and acted) more like you. That experience taught me how poor a strategy it is. The success stories via boycotts are a fairly small minority. Most attempts at change via boycotts fail. It's incredibly hard even to start one.
A lot of shaming is involved, and it rarely works. People don't like to feel ashamed. As he said in his response to you, it does quickly degrade to infighting amongst consumers and a lot of energy is wasted there that could be used in alternative strategies.
It requires people to be very knowledgeable, and I saw mostly failures even amongst highly educated folks. To understand an issue, connect all the dots, etc takes a lot of effort. Most people want someone else (government agency, consumer watchdog, etc) to do all the work.
That's not to say broad media campaigns are a bad idea - I think they are necessary. But much more often than not, companies will win on the purchasing decisions battle.