This book is interesting on the subject: https://amzn.to/2XxbbSX
reviewed here in The Economist: https://www.economist.com/business/2011/01/27/the-crescent-a...
If corporations cannot get those benefits, how will we as a society get any benefit from people working together for something complex? You cannot make a workable spaceship, car engine (a car might be possible once you have an engine that meets emissions, and several other complex parts). Our modern world is mostly designed around retirement plans owning corporations - without some legal shield 3/4ths of the US should go to prison for Enron
Will it be a few rich people who enter into all those contracts and pay their people? At what point do the rich refuse because they have too many people signing contracts on their behalf that they dare not take the risk?
There could well be other solutions to the problem. It could be that some alternative is a "better" compromise. However it is not easy to come up with something that doesn't have flaws that are worse than what we have.
So for example, with Citizens United, there's no restriction on individuals that make up the company from making political donations from their own personal funds - including those that they earn as owners or employees of said company. But the company cannot use the funds that it owns as an entity in its own right for the same purpose. If its owners want to use those funds for that purpose, they can have the company pay it to them as dividends (taxed accordingly), and then spend them as they see fit - with their own name attached to any such use.
Note that this effectively protects free speech qua speech even for corporations, because there's ultimately always a person speaking.
Then they would just not exist: a corporation is exactly a grant of legal personhood.
Governmental organizations are also incorporated persons, including governments themselves (otherwise you wouldn't be able to sue the United States).
Non-corporate entities like nonprofits, partnerships, cooperatives, educational institutions, etc are also legal persons, and need to be for the same reasons.