When you say "most people don't do it willingly", this implies that they're forced to do it by someone else, ie sex slaves. Deciding to do something, even if it's just to survive, is still doing it "willingly".
What you've quoted has nothing to do with what I said, despite the fact that it specifically says, "choice", which I put in bold. Not a lot of people are "happy" working in fast food restaurants and wish they could get a better job but that doesn't mean they're doing it "unwillingly" or even that they have no choice.
Also, given the "moral" stance of that particular source, we can safely ignore half of what they say anyhow.