First, you are talking about herbicides, not pesticides.
Secondly, GM opposition is a very odd thing. Every carton of milk I buy has a little sticker that it comes from non-GM cows, Every one of those stickers is a lie. We have selectively bred cattle for hundreds of years to build the modern dairy cow with specific genetics. It's been very scientifically done for a long time.
Third, the real issue here is not GM. It is IP. (I know Stallman would bristle at generically lumping it all under IP). But this new idea that one party can own a seed and just license it to others for planting is crazy. The idea that they can contaminate other crops and then claim ownership of those crops, too? Crazy.