Answer this: What's the difference between ejecting a small flechette from a railgun, and ejecting gasses via a rocket engine? The answer: There isn't any. The rocket engine simply ejects far more material. It's impossible for there to be an action without a reaction. The magnets are exerting a force upon the flechette (via a magnetic field), which means that the flechette must also be exerting a force upon the magnets (also via the magnetic field). The reason a monorail's track doesn't move in the opposite direction as the train is because it's fixed to the ground (and it's mass is substantially greater, though that would only slow the movement, not stop it).
If I were to be floating in space, and I were to take a wrench and throw it, I would move ever so slightly in the opposite direction, because just as I'm exerting a force upon the wrench, the wrench is also exerting a force upon me. However, you have to keep in mind that, in a zero-G environment, there's nothing to keep me from moving in a straight line forever (things in motion tend to stay in motion, and all that jazz). Now, even that ever so slight ammount of backward momentum placed on me by the wrench would become a serious problem unless actions were taken to stop my movement (ie: firing thrusters). Even lasers aren't above the laws of physics. One of NASA's proposals for a fast-as-light starship utilized a large laser beam directed from an orbiting satelite or ground station to "push" a cup-shaped craft. Granted, it would take over a decade for the craft to reach anything near it's top speed, but it proves that light, on it's own, can exert a force upon another object. Unfortunately, the project never got out of the planning stages.
-Keiichi