We, as humans, aren't well equipped to properly measure the impact of posting a lot of little things which, individually, don't give a lot of information away (if any). "Big Data" projects and tools such as these allows agents to learn more about us than we have ever consciously given away.

For example, if you post only about being sick, then about your craving for pickles, would you expect an agent to be able to identify that you're pregnant, and given your posting timeline, identify the due date with remarkable accuracy? Ad companies have been doing this with browsing behavior for awhile.

The only way to avoid this particular threat is to not participate at all, something you will have a ridiculously hard time convincing a teenager of.

About as much as you get when you say something in public space like a park. While potentially "anyone" can hear you, it's not going to be used against you 10 years from now to label you a criminal.

None. Schools should be teaching students the dangers of posting publicly, not fostering and then exploiting the ignorance.

What are we paying scholar for? To educate students!