If you haven't seen the movie "Food Inc.", I'd highly recommend it for insight into Monsanto's practices. Monsanto owns patents on their modified seeds and saving them, instead of buying them from Monsanto, is a patent violation. Problems arise when Monsanto's proprietary seed is introduced into an area and surrounding crops are cross-pollinated with pollen from the GM crops. Even though the cross-pollination is accidental, if a farmer saves seed for his next crop and any of that seed contains Monsanto's patented genes, he's in violation of Monsanto's patent. Monsanto is basically polluting farmers' crops with pollen from their unnatural crops, and then reaping a financial reward by suing farmers whose crops have been polluted.

To my mind, it's like patenting a disease organism, spreading it around, and then suing the people who get sick for having the organism in their bodies.