They signed the contract when they bought the seed. They entered the agreement willingly. No different then when you skip past the EULA on a video game saying you won't distribute it or crack it.
That...has absolutely nothing to do with patents. Or morality.
The contract is directly between the farmers and Monsanto; patents are filed with the government, and have force no matter what contracts exist.
And "they signed the contract" is a purely legal argument, it has no moral force. Particularly given your apt analogy to EULAs, indicating clearly that the large companies create contracts that are a) guaranteed to provide disproportionate benefits to them, and b) effectively impossible for laypeople to understand without assistance. Sure, it's legal for them to create contracts like this...but would you really argue that it's moral?
I said contract because you used patent incorrectly. You think the patent is what stops farmers from replanting but it's the contract and the licensing. The patent stops other companies from using the genes to create their own seed. (I'm incorrect here. Just took a look at Monsanto's patent page and they say they do use it to assert breeding rights. I guess the laws around DNA aren't defined enough for licensing and contracts alone.)
And yes it is moral. They are not under durress. There are plenty of competitive viable alternatives. The contract is very clear in the farmers inability to replant as so many are quick to point out. And all parties consented. Farmer gets a product, business gets money. Business makes sure they have a future by making sure the farmer doesn't regrow their product and sell to other farmers.
Tell me why it isn't moral. Are you advocating that patents and product licenses are immoral.
If a farmer unknowingly plants Monsanto seed because another farmer sold it to him. The purchaser can sue the seller for damages just like any other business. It has everything to do with contracts because the only people getting sued are the ones that have enough seed to plant a second crop. That second crop came from a farmer who signed a contract saying they wouldn't grow seed crops or resell their seed. So someone in the chain broke their contract trying to undercut Monsanto business.
