Because oaths and pledges are a little creepy, this effort needs something else—something that comes out of the legal and business worlds: a contract.I have several things to say about that.
1) Could we possibly confuse the distinction between an oath and a contract any more? One of the most damaging things that happened to marriage was that people started thinking of it as a contract -- which, of course, can be renegotiated at will by the parties to the contract, and which may even have breach clauses just in case it doesn't work out -- instead of the sacred oath in which God unifies man and wife into one flesh, until death do they part.
2) Why should an oath or a pledge be "creepy"? Does the language of honor frighten you so much? There is an honor interest at stake, actually, because the corporation wishes to join the polity in the sense of obtaining legal protections and at least property rights. That means that the company takes the business of the polity -- protecting the rights of its members -- to be a common good of which it would like a part. Why, then, should the corporate person not be bound in the same way as the ordinary person: that is by honor, so that loyalty is owed if (and only if) the state does its duty in protecting the rights it was constituted to protect? What makes corporations special, that they should not have to take an oath that properly expresses the relationship between citizens and the polity of which they are a member?
3) Perhaps your real concern is that corporate loyalty to the state sounds like fascism. So, you're a fascist to some degree. But the American project has used the fasces in its iconography from the very beginning. This kind of proto-fascism is not the same as the full-throated Fascism of Mussolini -- for example, it admits of limits such as the right to renounce citizenship, the right of revolution in the cases where the state ceases to perform the duties for which loyalty is the reciprocal reward, and that some of the rights the state is duty-bound to protect include freedoms of association, religion, the press, etc. That we intend to bind everyone together, 'E Pluribus Unum,' does not mean that we shall have 'everything for the state, nothing outside the state, nothing against the state.' Our version creates several areas that are meant to be outside the state, where the state is supposed to be bound not to interfere.
4) Of course you understand that this demand for loyalty raises the price of doing business somewhat: what you are imposing is an opportunity cost. That will have economic as well as political ramifications. You had better be clear on just what you are offering in return, and the deal had better be fair if you want the corporate citizens to accept it. For example, I've heard a lot of noise lately about trying to overturn Citizens United via legislation. If you do, you had better think carefully about what you will use to replace it. If corporations are citizens, they won't get a vote (unless we change the Constitution to permit corporate citizens one vote, in addition to the votes of their members who are American citizens). Nevertheless, you have yourself proven that they will have a legitimate interest in being able to express opinions about the government and its policy. That's one of the traditional parts of loyalty oaths, going back even to the feudal loyalty oaths: in return for loyalty, you have the right to advise on policy.