What if everyone could know every detail about any person? What if, Matrix-style, you could upload into your brain, on demand, every intimate life experience and detail about any person that you meet? Every weakness and insecurity, every sin and virtue, every insane thought and unrequited longing, every proclivity, kink and quirk, every scar and tattoo, naked and exposed? No fact about a person, in this thought experiment, could be kept private. Privacy simply does not exist.
In US: must be an attorney licensed and in good standing in any state, territory or DC.
Outside US: must be a lawyer or equivalent (eg counselor, barrister, advocate, solicitor), duly educated and licensed/accredited and in good standing.
As a general rule, experienced and currently practicing lawyers, and those teaching law in the legal academy, are more likely to be admitted.