And it’s that implied “promise” that is at stake here. Facebook has terms and conditions, but the implied promise to date is “we’ll let you opt-in”. There are subtle differences in approach with Beacon that break this.

And, although I honestly haven’t seen the commentary you refer to in terms of user’s rights, I think this is the core of the argument. When creating a big community site like this, there is a power-play at work. And when enough users revolt, it can have pretty intense results - witness the recent overtaking of Digg by it’s members over censorship.

Although legally Facebook’s T&Cs are sound and give them the permission they need to do what they’re doing, that’s not the dynamic or expectation of their community. And with that trust broken, Facebook has a real dilemma.

If they don’t re-structure Beacon to be truly opt-in, they risk a serious backlash that could really stunt their growth (I’m not suggesting they will collapse or anything as dramatic as that, just that the space becomes much less appealing to new and existing users, and they start looking elsewhere).

Yet if they change their approach, they risk alienating their advertisers at worst, or at best, reducing the value proposition of what is (honestly) a really interesting and innovative approach to marketing/advertising in the social media space. Which, of course, damages their ability to monetize the massive community they’ve built.

I’ve just finished reading an article in Fast Company, and the founders are innately aware that their user base is the only true asset they’ve got - so I think they’ll ultimately change their current practice to be more truly opt-in, or at least tweak the feature to resolve some of the more serious issues.

But it will be interesting to see how they approach it and how it resolves…