There is and can be no ethical principle [..]
I wasn't addressing the ethical part of your claim at all, but since you insist: there can be a moral argument in favor of patents. It goes like this:
* Corporations are legal entities that are allowed because they were expected to, and have been shown to, advance our average wellbeing
* Corporations more effectively increase our average wellbeing if they are encouraged to heavily invest in innovation. They receive this encouragement by allowing them temporary monopolies on their inventions, thus enabling them to profit from their investment
* On average, the population profits: they have more free time, more money, a better health and can engage in 'creating and trading' all they want, except for a few specific instances that have been sacrificed in order to enable them to have these resources and this wellbeing in the first place
It's a trade-off our government made for us, in the belief it would be a net benefit. Things seems to have taken a wrong turn somewhere, but the original intent of the patent system was for the public good. That is a valid moral argument. Which doesn't mean you have to agree with it.
