Do you have a source for this? Also, I think it would be considered spying. Facebook, the NSA of the corporate world.

I closed my account 5 yrs ago as well.

Many sites do this. They encourage users to give full access to their phone's contact list, and store all the data they get from it, then start building a network of "people who know this email address/phone number", ostensibly so that when they finally convince someone to sign up they have a ready-made network of recommended "people you may already know".

I imagine they try their hardest, and I can't stop them from doing that. But I sure as hell don't want to voluntarily help.