You should be afraid of having the social graph of half of the Western world on Facebook. You should be afraid of storing most people's email unencrypted, in only a handful of data-centres.

Then there is the progressive lockdown of the whole internet, where it becomes increasingly difficult to speak your mind, simply because it's harder and harder to get your own blog. I mean your blog, on your domain, hosted by yourself (or at the very least a virtual hosting provider). These days, it's Facebook, Medium… places where an overseer has the right to block whatever you write. A good thing in most cases, but at least we should be able to speak elsewhere.