Though I agree there is a two sided ownership (both friends own a 'side') why the privacy policy stinks to me is that it does not seem to me that Facebook really cares about this 'ownership'. They really only want more data and to make their site more valuable. Is it unfair of me to attribute a rationale to Facebook's decision without cold-hard-facts, perhaps.
However, lets look at the took cases 1) They actually care about this 'ownership' 2) They do not care.
In case 1), they are afraid to violate a person's privacy choice of having a friendship be public. There is essentially a tension between their privacy choices and their 'friends'. It seems to me that when two choices are odds like this, caution is the best route. For instance, when two people know a secret that relates to both of them, and one feels uncomfortable about revealing it, the general rule of thumb is that you do not reveal (unless its like murder 0.o). Overall, I guess it seems like if you do make it 'public' it makes someone uncomfortable. While if you do not, it makes someone not get something 'they want'. In this situation, just err towards caution and make it private. What does everyone else think?
In case 2), they just want more data. Well I understand it, but I do not really respect it. I think this is easy. Make it private.
What do other people think? I am open to any logically flaws you find with the above statements.
In the same way, if you're trying to keep yourself incognito...well, don't use Facebook. And, if you must use Facebook, then make friends with great discretion. Just like it's a good policy to only create emails/nude-selfies sparingly, and only when the occasion demands it.