If it'd be just as convenient to buy locally, I could. If the alternative was as easy as driving to the supermarket, no one would mind. People like convenience, and people are lazy. Facebook is very convenient, mostly since everyone is already there (all the groceries are close at hand). But the devil is in the details. However much you try to layer your interaction with Facebook, through whatever privacy filters you got setup, you'll still be a user on Facebook. And as such you'll still be contributing to whatever Facebook is. That's why I think there's a reason for a person who claims to stand with FOSS, and who argues for the right for integrity online, can't also claim that using Facebook is a viable option. Not if these are your concerns. Sure, I get the idea of the lesser of two evils. I'm just saying it's important to note how it's still evil.