"Using" - more like you provide information which is the price of admission. Same as it is with any other company providing a free service. Characterizing Facebook as "evil" for this is quite silly.
And much like email, you can roll your own. It's much harder, but it's possible.
If people are willing to give up their privacy to use facebook and find value in using facebook, i'm fine with that and i won't enter a jihad to make them stop using facebook, although when i can i try to make sure they are a minimum informed about what they are giving up (while trying not to be too insistent, just providing information).
As for you can roll your own facebook, this is absolutely false. Facebook tries to get the whole planet registering with them, and don't have and probably will never have a protocol letting a fully featured "facebook bis" integrate with them (except maybe if legally bound to).
e-mail is a completely distributed service. People using gmail are not segregated from the others.
Now I'm also not pretending that facebook is evil for all that. I was initially reacting at your comparison between facebook and e-mail, which made little sense.
