Prisoner’s dilemma: margins are razor thin. If your fellow farmers use better seeds then you are forced to use them as well. Otherwise you won’t be able to match their prices without selling at a loss.
That's true of any productivity enhancement. If your neighbors use more efficient tractors you're at the same disadvantage, but nobody argues that farmers should be able to steal tractors.
The parent has to do with permission, not stealing. Imagine if your neighbors could have an exclusive license to buy the new obviously superior tractor which you will never be able to obtain no matter what you do, simply because you're not them. This is legal today, the argument is that it shouldn't be because it punishes competition and lets the rights-holder wield too much power over the market.
No, anybody can buy into the Roundup Ready system; it's not exclusively licensed.
Only if the cost of monsanto seed + roundup is less than the cost of regular seed per expected harvested bushel? Otherwise, no one would use the monsanto seed + roundup?