One advantage that humans have would be strength in numbers. At the time of this writing, we have just over 7 billion people living on Earth, and that's a lot of people to fight against. The problem is, if machines decided to start a mass extinction, there could be a few survivors but wed never be able to re-coup our numbers. Simply put, it just takes too long for humans to reproduce. Nine months of pregnancy and then they wouldn't be effective warriors until they are at least 10 or 12-years-old. Even then, preteen soldiers aren't going to be the most effective fighters against the greatest enemy we've ever encountered. That is, of course, if the children get to 10. Giving birth and raising children will now have to be done in conditions that are worse than the Stone Age, and if they survive birth, they need to be protected and fed for the first part of their life, which will be much more difficult because people will have to scavenge for food in desolate wastelands along with the possibility of poisonous air, sickness from radiation and being hunted by drones. Life would simply be too dangerous to adequately protect children. Robots, on the other hand, will be able to mass produce themselves, battle-ready and with a single-minded goal to hunt down and kill humans. For example, researchers at Cornell University have developed a robot that is able to produce a copy of itself in two-and-a-half minutes - we would simply be overwhelmed by robots and lose before we could re-group.
