In the 1978 case Marshall v Barlow's Inc. it was decided that a surprise inspection by the Occupational Safety and Health Administration violated the fourth amendment rights of corporations. It was decided that surprise inspections were "unreasonable searches". Not only did the decision marginalize worker safety by denying OSHA the right to inspect a workplace for safe working conditions, but a chemical plant cannot be inspected without warning to ensure that it's not blatantly polluting. Do you live anywhere near a chemical plant? Think about it.
With the stroke of a pen, corporations didn't gain personhood, yet began to be treated by US courts as if they had.
What Opportunity did Corporations use to Pursue Personhood?
Following the Civil War, people of African descent were no longer allowed to be owned by Whites in any part of the US. Congress decided that, to solidify this law, an amendment to the Constitution was needed. That amendment was the fourteenth amendment and was passed and ratified in 1868.
Section 1. of Amendment XIV reads as follows: "All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the state wherein they reside. No state shall make or enforce any law which shall abridge the privileges or immunities of citizens of the United States; nor shall any state deprive any person of life, liberty, or property, without due process of law; nor deny to any person within its jurisdiction the equal protection of the laws."
Freedom would do those of African descent no good if they were not protected under the laws of The United States as full-fledged citizens. The fourteenth amendment was ratified to ensure that everyone in every state in the US realized that people of color were citizens of The United States of America and possessed all of the rights identified in the Constitution of The United States.
How Easily Was the Fourteenth Amendment Implemented?
That depended upon who or what you were.
Ironically, the fourteenth amendment did not recognize women as equal citizens as they had to wait until 1920 to gain the right to vote.
Inasmuch as the fourteenth amendment was for the benefit of the newly freed slaves, people of African descent had to spend almost 100 years after its ratification fighting and dying to actually realize the benefits of that amendment. It wasn't until President Lyndon Johnson signed the Civil Rights Act of 1964 into law that people of color began to enjoy the benefits of the fourteenth amendment.
On the other hand, corporations had to wait a mere 16 years after the fourteenth amendment was signed into law to be considered "persons" with all of the rights granted by the Constitution. Adding insult to injury, no law was ever passed and no court decision ever handed down which specifically granted personhood to corporations, entities which are not only not persons, but which, but for the grace of real persons, wouldn't even exist.
What the People Got
In the late 19th century and the early 20th century, workers in the US, especially immigrants who came to the US for a better life, fought and many actually died in attempts to organize against draconian working conditions placed upon them by American corporations and businesses.
These people fought for and gained the eight hour work day, the forty hour work week, a reasonable amount of time away from work, including vacation time and compensation for sick time. They also rid the US of the scourge of child labor. These were the early unions and, if not for their persistence and outright courage, those of us working today would not have the benefits we have today, whether our workplace is unionized or not.
However, despite all of the blood spilled in order to gain fairness for the American worker, the stronger the corporate person has become, the weaker the human worker's rights have become. Today, there is a backlash against unions which protect workers and, unbelievably, much of the attack comes from middle class workers who happen to work in non-union environments. Many letters to the editor lambast federal, state, county, city and/or town workers for the benefits they receive as well as the pay they receive. Instead of displaying the courage shown by the early organizers and pursuing what is rightfully theirs as workers, many people, again many who belong to the disappearing middle class, want no workers to have the benefits that were painfully gained. The workers, especially in the private sector and even more especially who are employed by multinational corporations, are seeing their pay and benefits dwindle, not to mention their jobs disappear. They respond to their losses by castigating those workers who've fought to hold on to the benefits gained long ago rather than fighting for the same benefits.
They are afraid that, if they attempt to organize, they'll lose their jobs. They don't have the presence of mind to realize that, if they don't organize, the corporation can shut them out at any time without notice so that those at the top of the corporation can increase their wealth. And as it stands now, a worker who's been wronged can take the corporation to court. However, as the corporation will be viewed as a person as much as the actual human worker who's been wronged will be viewed as a person, the corporation will claim in its defense that it's been wronged and, unlike the human worker, the corporation will be represented by the finest, most expensive law firm it can hire.