This is definitely an interesting thread, but there seems to be too much focus on Runyon as the bad actor in this case. While I can't say I agree with what Monsanto is doing (the suing and the GM component) I don't think the circumstance is reasonably accounted for...
Using Runyon as an example - even if evidence shows that he took advantage of the situation he was inadvertently involved. The root cause was not of his initiation. Ultimately, in my eyes, it should be the responsibility of Monsanto and it's customers to enforce containment. If that's not possible, then they have a flawed product. Monsanto is well aware of the risk involved in IP within a seed. It's main objective in it's lifecycle is to self-sustain, so unless they can turn that off without a doubt they have to accept the risk.
What I mean: If Monsanto and it's customers can't contain the product they buy and use then there should be no implications for anyone around them to take on that responsibility.
Example (and I know these haven't been going well, so my stab): BP comes knocking on Runyon's neighbor's door. They want to drill in his (the neighbor's) fields, but there is high risk that they may contaminate a shared water table Runyon and the neighbor's land is sitting on. The neighbor decides to go forth - and the inevitable happens. Now - who's fault is it? Runyon's - for being where he is and not instigating (at all) the actions that the neighbor chose to execute? In an argument where the outcome is bad - it's easy to identify the bad actor. In an argument where the outcome is indirectly good there is no incentive for Runyon to sue his neighbor for giving him something that normally should be paid for.
Solution?: Monsanto must place all risk of seed carryover on to it's customers. It is not the anonymous farmers responsibility to fight Monsanto when their competition (the neighbor) has instigated the problem. BUT... Monsanto would never sue their own customers because that is counter-productive; nobody would buy seed from them.
I agree with suing Monsanto. But on the basis that Monsanto and it's customers are operating under a negligent business model which enables them to sue innocent farmers. It almost seems to me that Monsanto is under the assumption that emminent domain applies to it's intellectual property - of which I do not agree.
If the BP spill would have leaked $20 bills instead of oil - you really think there would have been any lawsuits or complaints?
Bottom line: if Runyon didn't intentionally set out to steal Monsanto seeds then he has no responsibility to Monsanto. If you argue that he took advantage of the situation I would argue that is his right and luck. Now if he turns around and directly competes with Monsanto - there may be a case. Otherwise in the land of my personal morals I don't believe Runyon can be held accountable.
Carpe diem.
EDIT: Formatting. And thought... If Monsanto has the genetic research capability to create a product that is resistant to something like RoundUp - why can't it modify the lifecycle of the plant to only grow if some simple additive is sprayed on the newly planted field to "activate" it? Something along the lines of a license key for seeds. That way - if Runyon was caught with plants in an entire field it would showcase theft. It's easier for Monsanto to sue innocent bystanders than put money into R&D of a protection mechanism I would guess... And, yes, I've oversimplified genetic engineering, but again - it's a flawed product if you can't protect it.