They are looking at all the news - some places ban, and some places OK your boss asking for your facebook login. Or if you don't have a page, you aren't hired since no one can check on your social tendencies.
Your "friends" can ruin your credit rating. (I mean those that friend for quantity)
Law enforcement trolls and can entrap.
Social Media misused has driven kids to suicide.
Those that don't use are feeling secure, but probably use all the other goodies on the smart phones or follow other fashion not giving a damn about child labor or working conditions in other countries.
They are just as bad as those who use social media with all the hype.
There probably are more millions who do pay attention to the TOS and check their settings before using. For them, it's a convenience and we shouldn't be too much in either camp, either berating non or casual users for not telling all, or feeling so damn smug since they don't use it.