This phrase is also referred to as a presumption of law in Blacks.
So there you have. The reason that the "court" feels that it can deal with a fictitious entity called a person. This is a claim that stands unrebutted because for the most part, you are dealing with the effects and not the cause.
The next question inevitably becomes, how do we dissolve their ability to use this instrument against us? Do we verbally state this at the outset of a court matter? Do we rebut in writing? Do we wait until the appeal process kicks in and seek dismissal on these grounds? Is it a combination of factors? I would love to read your thoughts in the thread below, and who knows maybe between a few of us, we can nut this out to a workable solution because in my view, a tool is no good at all unless it can be wielded in a manner that benefits us.