"The great object of an incorporation is to bestow the character and properties of individuality on a collective and changing body of men." - chief justice Marshall
a few of these decisions to be aware of:
The Rev John Bracken v. The Visitors of Wm & Mary College (7 Va. 573 -- 1790 Supreme Court of Virginia) established that a corporation had the right to reorganize itself, ie, that the people working together for a common cause could hire+fire just like they would if there was a single owner
Trustees of Dartmouth College v. Woodward (17 U.S. 518 -- 1819) established that groups of people could enter into contracts and that they'd be enforceable just as contracts with a "natural person".
Santa Clara County v. Southern Pacific Railroad (1886) established that the 14th amendment (due process) applied to groups of people organized under a common cause, and not just to individuals. This is followed up in Pembina Consolidated Silver Mining Co. v. Pennsylvania – 125 U.S. 181 (1888) which rather explicitly states "corporations are merely associations of individuals united for a special purpose and permitted to do business under a particular name and have a succession of members without dissolution".
United States v. Auto Workers, 352 U.S. 567 (1957) upheld the ban on corporate campaign funding, but as is so eloquently noted in the dissent, "associations of manufacturers, retail and wholesale trade groups, consumers' leagues, farmers' unions, religious groups, and every other association representing a segment of American life and taking an active part in our political campaigns and discussions" should have "all channels of communication be open to them during every election, that no point of view be restrained or barred, and that the people have access to the views of every group in the community."
Austin v. Michigan Chamber of Commerce (1990) and McConnell v. Federal Election Commission (2003) extended the restriction on campaign funding to also cover advocacy, limiting the speech that could be undertaken by groups of people pooling funds together.
Citizens United v. Federal Election Commission, 558 U.S. 844 (2010) overturned the Austin and McConnell decisions. Justice Kennedy: "wealthy individuals and unincorporated associations can spend unlimited amounts .... Yet [under the Austin decision] certain disfavored associations of citizens — those that have taken on the corporate form — are penalized for engaging in the same political speech .... When Government seeks to use its full power, including the criminal law, to command where a person may get his or her information or what distrusted source he or she may not hear, it uses censorship to control thought. This is unlawful."