Firstly, Monsanto, Syngenta, and their ilk have dominated the world seed market since the 1950s. GM food is completely independent of them. Monsanto may be the largest US producer of GM seed today, but the next generation of GM plants that are being worked on are designed to solve a wide range of humanitarian problems. Please, don't make your mind up about a technology with myriad potentially life-saving uses based on one company's commercial implementation. They don't define plant science.
Secondly, the jury is emphatically not still out on the consequences. As with climat change, in the independent scientific literature there is an overwhelming consensus that the technology itself is fundamentally safe, that each new implementation must be assessed separately, and that the risks in general are lower than those for conventionally bred crops.