As to your first argument, I don't think it's quite the same. This is like saying that when I buy a song I can freely resell it. Farmers aren't buying the crops and using it for personal use and giving it to friends for personal use. They are buying it and selling it on the open market.
If I personally went and bought Monsanto seed and used it for my own plants the I ate/gave away and gave it to friends who all used it for personal use, Monsanto would be hard pressed to stop me/they probably wouldn't bother.
Monsanto's lawsuits against farmers are aimed at farmers that did not buy Monsanto seed.
Monsanto says that because their seed and their plants are growing on a farmer's land, that farmer must have stolen the seed and is benefiting from stolen property. So they want a cut of the gain from the stolen property.
The farmers say that pollen goes where the wind blows it and plants and their DNA spread naturally. The farmers say that they did not intend to grow a Monsanto product but because the Monsanto products grow in greater densities and are more robust than naturally growing soy and other crops, the Monsanto products crowd out the farmer's naturally growing products.
If I personally went and bought Monsanto seed and used it for my own plants the I ate/gave away and gave it to friends who all used it for personal use, Monsanto would be hard pressed to stop me/they probably wouldn't bother.