1. lowered levels of food production have their own averse effects and risks, notably, famine and starvation. herbicides, persticides and monocultures of high yield strains are widely believed to be responsible for saving a billion lives. if you eliminated those things from the planet right now, hundreds of millions of people would starve next year.
2. the things you're talking about aren't monsanto's fault. people are doing business with monsanto willingly. you don't have to buy gmo seeds (or any seeds) from them if you don't want to.
> Is it possible for a group to select and breed their seeds over years, and eventually having a breed that is similar to a patented Monsanto seed?
sure. if you have a breed similar to a monsanto seed, they'd win a lawsuit against you only if your breed had the same gene that they patented. you may think that that's not fair, but that's how things work. if i win a patent for a space engine for interstellar space travel, and you independently invent the same engine, i'd also win a lawsuit against you. also note that no one has actually bred a RoundUp resistant strain of plants independently of monsanto.