Earlier quoted context omitted.
> Why do you free work for a for-profit social network They don't. They do the work for a community they're part of. The social network hosts that community, and tries to make a profit doing so. I organise a meetup that's held in a pub (well, not at the moment). People coming to the meetup spend money on the pub's beer and pizza. Am i doing free work for a for-profit public house?
Yes you are. Social organizers, advertisers, trend setters, ect frequently get free product, kickbacks or some money for their 'work'. That's the work you have done. It's not your intent to do work and it's probably not the pub owners desire to pay for meetup organizers, but regardless of your and the pub owner's intent, work has happened.
The option is to do "work for free" or to shell out hundreds of dollars.