What happens when something was supposed to be private but is accidentally posted in public? Or if a friend turns around and shows the boss a screenshot of something an employee said? What is really private?

Please develop and defend your point of view on the following issue:

Should schools and employers be allowed to use material found on persons social media sites Facebook, Twitter, Tumblr, Steam, etc. as grounds for disciplinary action and/or deny them a job/admission? (This topic assumes that the information is obtained through public searches, not hacking or other illegal activity.) What happens when something was supposed to be private but is accidentally posted in public? Or if a friend turns around and shows the boss a screenshot of something an employee said? What is really private?

Try to support your discussion with examples and evidence when possible, even if your supporting points are theoretical or hypothetical. You must choose one side or the other avoid sitting on the fence as much as possible.