Should a person’s social media

Should a person’s social media be considered by school admissions, police investigations, and potential employers? (Why/Why Not)

Police, definitely.
Employers, their choice.
Schools, no; admissions should be by merits and skills, not behavior.

Yes. To me if you put it out there then you are okay with people seeing it so you can not cry foul if someone actually reads it. If it offers an insight into one's behavior or clues to what can be expected from a candidate then that is what it is there for. If you don’t want people snooping in your business then don’t put it out there.