>Is Facebook really a "direct participant" if I have no way to know that their widget is even on the site until I visit it, at which point they have already participated and I have no way to avoid it?
If you meet someone at some office for an interview or a negotiation or something, and a third party is there whose presense was not announced beforehand, aren't they a "direct participant"?
And didn't you also had "no way to know that they would even be there" until you visited that location?
In the example you gave, I have the opportunity to interact with this third party, demand to know why they're there, and may choose to leave, with my privacy intact, if I don't like their presence. This is all part of the process of informed consent.
Clearly this analogy, particularly with respect to "informed" and "consent", does not apply to a Facebook widget on a site.
If you meet someone at some office for an interview or a negotiation or something, and a third party is there whose presense was not announced beforehand, aren't they a "direct participant"?
And didn't you also had "no way to know that they would even be there" until you visited that location?