I do it by getting involved in legislative processes - writing to, phoning, and meeting politicians and finding and encouraging others who also want to do this. I'm a lobbyist, by hobby and by profession. Mostly against software patents.
Others do it by writing free software. Eben's talk (which will soon be online) talks about a particularly necessary change we need to make to society, which can be done mostly by software development.
Voting will never give us a freedom-respecting social network :-)