I think the point is that the simple presence of a Like button tells Facebook that you've been there. You don't have to click it, you just have to load it. HN comment history is active participation.
And that's exactly what some of us do. But there's no way you're getting all of your facebook friends to do the same. Facebook can build a profile on you based on your friend's tracking data. Whether it'll be accurate or not is mostly a technical question - whoever looks at it will assume it's accurate. There are a lot of nefarious uses for this information and there's no useful way to opt out right now, short of not having created a facebook account. Hence the whole "mass surveillance" bit.
