The laws underlying corporations are based on the principle of individual rights. That is, the basis of a corporation are the rights of the individuals who form it. Rights are not fictional, and neither are the laws that a corporation must abide by. These laws are neither intrinsic, nor are they subjective and a matter of whim: they are objective facts that must be discovered (deduced from the basic principles while inducing the relevant facts) within a framework of rights.
The laws governing a corporation are the standardization and explicit recognition of the application of individual rights by the government. The laws protecting the right to free speech are not “legal fictions” created by the government but are laws based on this right. For example, if I can sell you a good, under the condition of “limited liability” — well so can a corporation. If it is illegal for me to pollute your home (pollution being a violation of rights), then so iis it illegal for the corporation.