more generally, "corporate personhood" in US law, going back to at least the 1790s and in other countries going back even longer, serves the legal purpose of establishing that when people work together to do something under the "corporate" banner (which allows them to have a succession of members working toward a common goal and pooling resources), they retain rights like speech, property ownership, and ability to enter into or terminate contracts including hiring and firing employees. This connects to the idea (expressed by chief justice Marshall) that "The great object of an incorporation is to bestow the character and properties of individuality on a collective and changing body of men."

Sheesh I wish I had read your response before posting my own. This more succinctly captures what I'm trying to say.