Corporate personhood is the easiest way to allow corporations to enter into contracts and engage in civil litigation. I'd be interested in what opponents of corporate personhood propose as ways around those problems, which I think are goods. Having to renegotiate all contracts with a business if the owner dies doesn't seem very efficient.

With regard to tax law, accounting is generally different between corporations and individuals. Specifically, individuals use cash accounting while businesses frequently use accrual accounting. Furthermore, businesses can deduct far more in expenses than an individual. One can argue about that, but I think it makes sense when you realize that corporations are ultimately owned by individuals, but individuals cannot be owned by other individuals or corporations. Individuals are ultimately the "base case" of ownership, so I think the different tax treatment of revenue/profit/income makes sense.