Also, you are using misdirection. Corporate person hood refers to more than the ability to hold a corporation liable. It refers to giving the corporation rights and protections in addition to those already enjoyed by the individuals who make up the corporation.
The ability to enter into a contract necessarily implies you have rights to own property, and trade that property with whoever you wish. Corporations have just as much right to buy or sell bananas or advertisements or widgets as I do.
The concept taken to it's extreme would give my wife and I (who now hold control of a corporation) an extra vote in an election.
In the US, votes aren't given to persons, but to individuals who are citizens of a certain age, and possibly other restrictions depending on state. Do mind the semantics, because corporate persons obviously don't fit in here.
If a different standard for voting was used, e.g. "Property owners cast votes proportional to how much land they own", then yes, corporations would cast votes. This is how it already works for voting for membership of corporate boards, so I don't see a problem with this. Obviously, that's a big "if".
Most importantly, from the liability you aspect you mentioned, is that instead of my wife and I being responsible for the crimes we collectively commit under the umbrella of that piece of paper, the paper is liable. We can do all sorts of unethical and evil using it's name, then fold that paper up and put it away if it doesn't all work out.
I'm not sure what you mean here. Marriage means you and your wife are considered a single person for certain purposes. Even if you have an LLC, you can't commit fraud - that's criminal, and you could be individually found guilty.