I don't think privacy should be an 'all-or-nothing' proposition; waving away your right to privacy should not be a decision an individual has to make. Ever.
I believe that what the majority of users want when interacting with internet platforms like Google, Facebook, etc. is a responsible use of their data; a reasonable balance between giving up information and receiving benefits in exchange.
From that perspective I would argue that Facebook collecting data from you simply by 'browsing-by' a like button is unacceptable. But I wouldn't go as far as to say that everything is fair after you've given alleged, implicit permission by clicking a button either. It's about a reasonable expectation the user has about what kind of terms he's entering into by 'like-ing' something. Is it okay for Facebook to have a look at what site your coming form? Associate your account with this like? Maybe. Would it be acceptable for Facebook to go through your history and look at the most recent porn sites you showed interest in? Probably not. That goes at the notion of contextual integrity you mentioned. The line is blurry but it certainly exists.
Another important consideration for me is who has access to the data that is collected. Larry Page famously answered to Paul Buchheit that there 'are no privacy issues' when faced with thousands of complaints concerning Gmail. I don't really mind machines going over the contents of my email in an effort to target ads at me. It's creppy to some but if you understand the underlying technology I would side with Larry and say that, really, there are no privacy violations. It's about the trust you have in a corporation when it comes to handling your data. Transparency goes a long way.
Give me your thoughts.
P.S: I don't think an individual or a corporation could successfully operate on the internet while strictly adhering to the three standards you mention. Getting explicit consent for every data transaction that occurs when using the internet would make that medium virtually unusable. We have to make certain, maybe gullible, assumptions about the companies and individuals we interact with to navigate everyday life; you do it every time you enter into a contract without studying the fine print.
A custom Facebook Share button sounds like a terrific idea, open-source it! :)