A. If I move a large hula hoop over your body, you don't go flying out the other side. Portals are just large hula hoops with either side in different places.
A hula hoop would be two portals facing opposite directions.
Not the same scenario at all.
First portal accelerates the object, second traveling in the opposite direction decelerates it equally resulting in a net zero.
If the second portal doesn't move with the opposite direction or speed, then it won't cancel out.
The moving portal would have force exerted on it in order to equal out the energy of accelerating the victims