Arguing that corporations should be legal persons isn't very popular, although Pol Pot and Stalin and Mao were popular, right until the lack of any restraint on govermental power wielded in the name of the People got a lot of people killed, in Stalin's case by a belief that central planning could determine agricultural output and distribution more efficiently than the New Economic Policy of basically market driven agriculture, a belief which killed five million people by famine.
See The Harvest of Sorrow for details.
That's not an argument for pure laisse faire either, and in fact no modern country does not intervene some in agricultural markets, although very often with rather perverse results, like paying people not to grow crops and punishing them if they did so to feed their own family, the latter an example cited as the ne plus ultra of the Commerce Clause, if something that ought to scare people as to its implications of the State being allowed in theory to starve someone to death.
That was also something of a weird case, and hard cases make bad law.
But as to corporations, the Left has made much hay lately of smashing corporate power without considering any of the history of why it is that corporations came to be legal persons, if the Right ought to take more seriously the "agency issues" of corporations too. (The agency issue with corporations as usually discussed by economists is that the Agents are the managers of the firm, tasked with maximizing the Principals, the Shareholders usually, utility, although with imperfect monitoring, that might not always be the case. For example, if bonus structures are too short term, one might have a JP Morgan trader find it in their interest to gamble with firm money in a way that is adverse probabilistically speaking to shareholder interests, which is why there are reasons to regulate corporations, if carefully.)
As to why we have corporations as people, in English law, originally it took an act of Parliament to make a corporation, say to pool resources to build a toll road or bridge.
That is why the corporate form exists in no small measure, to achieve objects that individuals would be very unlikely to achieve on their own, even if Adam Smith identified, correctly, other problems that emerge with corporations as to Agency issues, if he overestimated those problems as to evolutionary fitness.
In any event, because Parliamentary acts were required, and later in their American descendants State bills of incorporation were required, there was much corruption of legislators, since there was enough money on the table as to net profit to make it worthwhile bribing legislators to pass the acts.
Unless you think that the State should allocate all Capital, like Stalin, then having many actors pursuing their own interests is safer, since their interests won't always coincide. What is good for hospitals for example is not the same thing as the drug industry, since much of what they do is potentially rivalrous in character.
That doesn't make corporations democratic internally, in fact far from it, but preserving many different centers of power is better than one center of power as to preventing Stalin.
Eventually, the English realized the corruption of the way economic entities were created under the corporate form, and allowed for free incorporation as to not requiring anything more than a simple legal procedure. The United States adopted this mainly by the example set by Justice Story in Massachusetts in the 1840s, although Marshall set the ball rolling in the Dartmouth case, because every university is a corportation too, which most economic historians would agree helped facilitate the industrialization of the United States.
Maybe the Amish were right, although if we try to reverse that process, one would expect the population to fall dramatically too.
The formalization of the notion of corporations as legal persons was somewhat curious as to having rights protected under the U.S. Constitution.
Santa Clara v Southern Pacific Railroad (1886) is usually regarded as the central case, if it was somewhat obliquely addressed.
Something so deeply rooted in American history ought to be treaded with grave caution. One could argue that a very narrow Amendment to limit campaign contributions by for profit entities would be feasible to do without creating the Soviet Union, although to totally abolish the legal personhood of corporations would be a truly awesome step as to taking away any freedom of association, as Planned Parenthood is a corporation, as in careful what you ask for with all this enthusiasm lately of abolishing the legal personhood of corporations.