The idea of a Legal Person in contrast to a Natural Person has its roots in the need for a corporation to be able to to contract and to sue and be sued.
The United States has a strange relationship with the quaint dialect of English they use, with its old fashioned spelling and bizarre proliferation of rules and mnemonics to impose a pretence of order on the chaos of arguably the worlds most dynamic and nuanced language. Their dictionaries don't document the way people use language, but rather legislate on correct usage, condemning inovation as deviation. This is reflected in their culture in many ways: Biblical Literalism, based not on careful study of Hebrew and Aramaic and Greek and Latin, but on Johny come lately English translations, many drawn largely from the King James Bible, which while great literature, at best a peculiar translation of the deeply flawed Vulgate; Belief in the literal existence of not just a personal little-voice-in-the-head Jesus but an equally real (and external) Satan; Belief by half the protestant clergy in a "young" earth, code in too many cases for a belief the world is absolutely flat. This pops up in the most unexpected places, attempting to rewrite reality to confirm with flawed, limited and outdated uses of words.
The US Constitution grants certain rights and privileges to Citizens. It restricts the full privileges of Citizenship to a small minority of the population, and over the last 2 centuries that has been expanded to include many classes of person as citizens and to offer some rights to non-citizens. Fundamental to the contract with the states embodied in the US Constitution is that the Citizen is an Adult, in their right mind, possessed of free will and able to act free of co-ercion or the will of another. What is peculiar is that a Corporation is, fundamentally, not a free adult in full possession of its faculties, but rather has aspects of a slave, or a minor, or a person of limited mental capacity or awareness for whom a guardian has been appointed by the courts or a power of attorney exists created in better days against need.
A Corporate Person cannot decide to sue someone, that decision is taken by the Directors (or at the smallest scale the Proprietor). A Corporation cannot swear an oath standing in the docks, a proxy appears bearing notes and records just as would happen if Grandma were in a facility for the terminally bewildered. A Corporation is owned, fundamentally it lacks both free will and freedom of action.
A Corporate Person has no rights, despite the madness of attempting to apply the rights of a (natural) person to what is in essence a legal shortcut. A Corporate Person does have obligations, both the obvious fiscal ones to pay taxes, debts and compensation for wrongs, and the more nebulous but more important one to work within society towards the goals of society. That obligation can be summed up by Wil Wheaton's immortal words "Don't be a dick."
