You don't patent something because you built it. You patent something because you think someone else might build it, or because you don't want someone else to prevent you from building it.
After all a company that has 600 million users has a responsibility to make sure all these people are not put in harm's way. Just imagine how Mark Zuckerberg's feelings could get hurt if even one of his users ("the dumb fucks") were to be taken advantage of by some evil, data greedy, ad funded search behemoth.
And isn't it completely obvious that Facebook, unlike other major Internet companies, has no interest in tracking users? What on earth could they possibly do with that tracking data? Sell targeted advertising? No no no, Facebook isn't _that_ kind of company! And doesn't their track record of honesty and openness speak for itself?
Fundamentally though, I think your point is, "I don't trust Facebook because of statements and privacy mistakes they've made in the past." That's a fine opinion to have (even though I obviously don't agree with it), so please, for the sake of discussion, state it like that instead.
Edited to add that, in response to your first point (the non-sarcastic one), it doesn't necessarily imply an intent to track users. Filing defensive patents is nothing new at FB (Facebook patented the News Feed and hasn't yet sued anyone for infringement).
And speaking of obscured points, what are you trying to say? Are you saying Facebook is _not_ working on an ad network that does cross domain tracking of users and displays ads based on social graph data, and this is simply a defensive patent? Or are you saying they are developing this feature, but we should trust your company to not abuse it?
Shame on me, but I don't follow Facebook's announcements about privacy enough - it never even occurred to me they'd deny something like thi Just like Google started out monetizing the semantic graph (and providing them an superior search engine in exchanges is their goal. I thought that was the whole point, and the reason behind the $80B valuation (ads served in a Google like way using the social graph instead of the semantic graph). It just follows that this would require a certain degree of integration between ad partners and user tracking.
ps -I'm not trying to single you out and lay the blame for all my gripes with Facebook on you, I hope it doesn't seem that way.
So, beyond understanding the skepticism, I actually think it's really important, and personally[0] encourage it. We're not going to get better at privacy if people don't jump our shit over every perceived misstep, because we've either failed to make the right decision, or we've failed to communicate our decision effectively.
All I'd ask is that we try to keep this communication as high signal as possible, and avoid going down roads with no plausible resolution[1]. I think that's best for Facebook, the internet, and discussion in general at HN.
[0] I speak for myself and not my employer, Facebook Inc, blah blah blah.
[1] If you think Zuckerberg is evil and that we're all just going to try to screw you, there's nothing I (or anyone else) can tell you that is going to change your mind.
Nothing you can say, perhaps, but here's something Facebook can do: establish a years-long history of having new privacy options/controls default to the setting which reveals the least information to other users. Doing that for several years should help Facebook overcome their reputation for not doing so (a reputation which it has for a reason).
The reality is also plain to see for anyone who knows the least bit about web technologies. The way they designed their like button, their logout, their privacy defaults, etc is just too obvious and their public lies are a calculated attempt to mislead people who don't have a clue how these things work.
Seriously, I'm not trying to be a Facebook PR drone here, I just want HN to not suck, and one of the reasons it didn't suck before was the lack of snarky crap.