I agree, competition would be nice, and I also do care about privacy and not being the product.
However, being a pragmatist, I also see that FB has won a particular war: it managed to get everyone and their mom on it, and privacy issues are not enough to persuade 'the masses' to move to another platform. Proof being that almost no-one has left FB and that other social networks like App.Net, with all their marketing might, have failed to capture any relevant share.
For a competitor to succeed, it would have to offer something vastly more tangible to the masses to persuade them to swith. Google tried and failed, Microsoft tried and failed, countless others tried an failed.
FB had it relatively easy compared to anyone entering the market now: there was no real social network when FB started. Of course, there was MySpace, and a few smaller competitors, but almost no-one was on social apart from a few early adopters. Now, outside of China and probably Iran, practically everyone with a phone or a computer is on FB.
Offering just another FB-clone with a nicer design is not going to make people switch. Unless there is a killer feature, practically no-one apart from a few of us in technology are going to quit FB.
People have their lives invested in FB: it's where they announced their weddings, their first child, where they shared tons of pictures with friends and family. It would take a lot for them to move en masse somewhere else.
All I'm saying is that instead of attacking FB frontally, these new social networks should target smaller, more focused, markets, if only because there is a need for better experiences for people who are passionate about something.
That analogy with milk is a bit weak if I may say. A slightly better one would be to compare social networks to newspapers and magazines. FB is like your local newspaper, full of a bit of everything. Now if I want to get science news, I'd rather pick-up Scientific American or Nature.
There shouldn't be just one social network, that's my whole point. I don't want another FB, I want others networks where I can share and exchange with other people who share a similar driving interest.