With strings attached. It's like giving someone money & telling "you can only buy products that I approve of...". (Missing fine print: we will track you and trap you into buying these for as long as we can).
No matter how much they twist the motivations, given their history, I've no faith in them doing any good, except for their bank accounts. It's one company that has shown utter disregard for the privacy of their users.
The primary aim of internet.org is to map and build a deep graph of every living being and bolster Facebook's monopoly. In the short term, some might applaud the "free" internet carrot but the whole concept is detrimental to innovation in the long term. Either provide "real" internet without any strings attached, or else don't be surreptitious about your intentions and claim to do it for the good of humanity.
Billions of people would be happy accessing the free-but-limited internet and wouldn't have any privacy concerns. However their privacy isn't the only issue here. The problem is that these people would be unknowingly contributing to the success of the walled garden developed by FB & friends. In the future, companies aligned with them will have access to a trove of data & eyeballs. Those that aren't aligned or want to compete with them, would be shut out. This is anti-competitive. One might argue that without internet.org, these people would not have contributed anyway. However, the premise of "free" will result in a lot of paying customers to switch. And, many of those who don't have an internet connection today, might get one in the near future. One that's low speed and perhaps subsidized by the government. To understand that, you have to look at the growth rate of mobiles in 3rd world countries. The bottom of the pyramid does contribute to the success of many tier-3 cellphone manufacturers. There are people who earn less than a dollar a day but they stay connected with a mobile phone. With a connection that's not limited by any corporation.
As the old saying goes, "there's no such thing as free ...". One way or the other, someone has to pay for the internet. It's not going to come out of the FB shareholders pockets. The question we need to ask is, who is actually paying for it and what's the actual cost (not literal cost) to this freebie.
It would be a lot better if the government or a neutral organization like Mozilla takes up this initiative. I would be happy to contribute to an initiative that provides free or subsidized internet to the masses. An internet, where there's no restriction on which site you can visit. An internet, where nobody will track you or collect your data or re-sell it.