Well, they can't buy such seeds at the elevator like they could 100 years ago. And now they can't plant elevator seeds period, without paying the Monsanto tax. (I know that isn't the explicit text of the ruling, but it is certainly its result for the most marketable crops.)
My grandpa's small family farm has been doing just fine without for decades, after all.
Yeah I'm sure his unicorn herd is thriving. If you actually have a family connection to agriculture, you know that outside a few sheltered crops like avocados, "family" farming has been steadily supplanted by corporate farming. I'm not against that per se, because competition, but my point was to impeach the oft-repeated lobbyists' saw that USDA is "for the farmers! [and their children!]"
what's the incentive to develop "superior" seeds if the first farmer who buys them can farm them and resell them at a lower cost until the end of time?
Monsanto already make a killing selling Roundup, to which these seeds are a completely complementary good. If Monsanto were good at business rather than evil at business, they would increase the price of Roundup and give the seeds away. (That would still be bad for both the environment and agriculture, but it wouldn't be as bad.)
this decision makes its harder to introduce those supposedly-evil GMOs in our American farms
News flash from the mid-90s: GMO crops are here already, in fact in many areas most farmers use them; that's why you can't avoid them at the elevator.