Consumers already can do that — they can refuse to use FB products — but they don’t. So a consumer group is pretty useless without enough consumers to actually exert their power.

This is exactly right. Consumers could organize a week without Facebook event, including deleting the app from their devices. If a significant number of people participated, FB would get the message.

Boycotts aren't the only option.

Consumers have boycotted products in the past. Consumer pressure has worked against Facebook in the past.

I agree that it is an unlikely and difficult solution. I don't see an easy one.

I am boycotting Facebook, but I only interact with 5% of my 'friends list' on a regular basis, so it's hard to get the message out, y'know?