Based on the first-hand statements from Obama's campaign manager [1], I don't think we can characterize how they got the data as licit. It was, at the very least, wink-wink-nudge-nudge under the table. Facebook either really did know they could do that and didn't care, or their surprise was genuine, but they didn't stop it. Nor did the campaign have permission from everyone. Nor were they any more subtle as to how they used it.
To the extent that there was no deception in the Obama's campaign's usage, it was because there was no communication at all. This is not an improvement! And they got more data from this "no communication at all" than CA did.
Yes. Everyone was doing it. I totally agree we have a systematic problem here. But everyone was doing it and we have a systematic problem here works in all directions at once. Trump can't be singled out.
In fact, Trump may not even have used the data significantly [2], which makes it even more blatently obvious to the rest of America and the world that it's not a matter of principle, it's all a matter of who did it and whether or not we can tar certain people with it.
The question I have, and rather a lot of watching Americans and even the world have, is: Does "Silicon Valley" care about our privacy, no matter who is violating it? Or is "Silicon Valley" only suddenly concerned because the wrong people may tangentially have gotten something out of it, but when the "right people" do it Silicon Valley will do everything in its still-considerable power to cover for them?
One answer leads to beginning to recover the respect the public even quite recently had for Silicon Valley, but may require a lot of people in Silicon Valley to admit that, yes, "their guys" have been abusive and some corrective actions may need to be taken. (And for quite a lot of people, not just an ambient "yeah, some other people need to do something but not really me" but you, you dear reader, need to understand that abuses occurred and stop covering for them because they were done by the "right person".)
The other answer leads to a world in which this week was merely the warning shot in a war that Silicon Valley is basically structurally doomed to lose [3], no matter how invincible it may feel right now, and proving to the world at large that all their fears about Silicon Valley are completely, 100% justified. Which is it going to be? The hard way that's right in the long term, or the short-term psychologically satisfying answer that leads to doom in the long term?
[1]: https://twitter.com/cld276/status/975565844632821760?ref_src...
[2]: https://www.cbsnews.com/news/trump-campaign-phased-out-use-o...
[3]: Vast, vast quantities of Silicon Valley power and money are tied up in the premise that even now only a vanishing fraction of their market power has been exploited, and the best days are still ahead. If America and the world at large (the vast, vast bulk of which is not Silicon Valley liberal!) decide that Silicon Valley is the enemy, then all the stock valuations for things like Google and Facebook will more-or-less turn on a dime from "Companies that have immense growth potential in front of them" to "Companies very likely to be in short-term decline". The stock market carnage and loss in power and prestige that will go with that will be historic. Silicon Valley would be well advised not to play with this fire.