Farmers are free to enter into this relationship since the seeds do conver some advantages in reduced use of pesticides etc. but there is a significant problem with cross-contamination from neighboring crops and through the supply chain so Monsanto ends up suing farmers who never had any intention to use their products in order to get everyone to bow to their will and maintain the agri-business model.
UPDATE: There was supposed to be some form of "terminator" gene included in the GM products to explicitly prevent generation two seeds from being replanted. I guess since we are talking about law-suits that did not really work as expected.
http://en.wikipedia.org/wiki/Genetic_use_restriction_technol...
Also the area in which Monsanto operates is one where most people IMO would want the old ideals of scientific discovery and invention returned to the common to grow the whole wealth of mankind - not artificially inject a trap such that one company extracts profits at the expense of wider growth
The problem is not that there are mega corporations making GMO seeds or mega corporations creating new drugs. The problem is the extensive patent rights on the result.
http://nature.berkeley.edu/~miguel-alt/modern_agriculture.ht...
Additionally, I don't have my contract with me at the moment, but I seem to recall the requirement of planting a percentage of non-GM crops as part of the agreement of using said seed. Planting RR crops year after year on the same ground doesn't work very well.