Yes, people sharing information and thoughts freely is a terrible threat to privacy.
Straw man. He's not arguing against the act of sharing of information. Read, then understand, then formulate your counter-argument.
Oh wait, no, the other thing - they (I should say 'we' as a facebook user) deliberately share this info and WANT to make it public.
That's an assumption that doesn't hold in practice. People deliberately share information. Who they intended to share it with and who it is actually shared with are not necessarily the same. A Facebook user may not realize the implications of posting something to a public page or a public profile, and in the process share more about themselves or their actions than they intended. You also fail to realize that the "big-brother fetish" is in fact a legitimate concern. Think about location check-ins. If someone else checks you in, Facebook now knows where you were. Did you want it to know that? Did you know that you can disable others' ability to check you in? Did you know that that gives Facebook one more piece of data to target advertising towards you? Maybe you do...but it's unreasonable of you to expect the masses to know all of the possible ways a simple click on Facebook can be used against you.
If they've stopped distributing the software, are they compelled for some reason to continue distributing the source?
They're still distributing it on their website, only for Ubuntu Desktop and Fedora 14/15 though.