I think users simply don't know enough to understand why their privacy is important. As such, my guess is that privacy concerns have hurt Facebook as much as they will already. This isn't the first or the largest instance if Favebook violating users' privacy.
What's more insidious at this point us that Google is only marginally better, but a lot if people have much higher opinions of Google.
When it comes down to it, trusting a company just isn't a good idea. Companies inherently aren't trustworthy. Even if the current leadership is trustworthy, companies can change hands and the data is still there. Companies get hacked, try to do what's right but compromise to stay in business, etc. The only way you can trust that a chat service isn't sharing your data is if they mathematically are prevented from doing so through cryptography.
Privacy is one of the main points any facebook competitor can use to get an advantage. One day that could really hurt facebook.