The “corporate” form of a business (as supposed to a partnership or other structure) is mostly a matter of taxes, legal liability, and the manner of raising capital and distributing profits.

Powerful unions are typically larger than the workforce of any one single company.

It's an extreme disruption in the economy, with all predictable consequences for productivity.

As for corporations and common law, that's a relatively minor deviation from the free market that would be almost entirely ameliorated by removing limited liability from tort cases.

>>As long as we're going to allow collective action by business owners, it's only fair that we allow collective action by workers.

Collective action is not the problem. Laws prohibiting employers from exercising their right to contract liberty and free association, to fire workers who unionize or strike, or to negotiate with workers not in a union, when a union has voted to collectively bargain, are the problem.

Like I said, the state gives unions a monopoly over any workforce in which they form. Giving a party a monopoly by restricting the contract rights of other parties is entirely different than "allowing" a monopoly to exist.