"Well but you decided to be born, and live in society!" Is not the definition of "you entered a voluntary contract" that most people would use.
Just admit that your initial response about contracts, was wrong.
Instead, you shouldn't have said anything about voluntary contracts, and just said that you support whatever the law says and the governments monopoly on violence, no matter what, because "democracy" or something.
So this part here:
"If you want to do whatever you want with your field, don't enter into contractual agreements where you agree to follow certain rules."
This part is not possible. No someone cannot do this. So you suggesting that they go do this, is wrong. Just admit that.
You don’t need a license to use patented technology which you either bought from a third party, was given or has blown onto your land by the wind.
The farmer had not entered into any contract with anyone, that is the point. It's not his fault if pollen from his neighbor's field entered his field, even if they contained "patented" technology.