I would agree that the argument is consistent with the fact that a remote observer can never observe a macroscopic object cross the event horizon of a static metric case of a black hole. However, It does the time/space dilation effects you use in your argument are not the same for the case of a dynamic space-time geometry. Also in the case of a static metric it does not prove that the event horizon will not be crossed in a finite proper frame time. It takes forever in a remote observer's time frame, but the time is finite for the falling observer. In fact, if the black hole has any charge it will give rise to a gravitational repulsion that is inversely proportional to the cube of the distance from the center. If the object is neutral in charge, it will throw it back out.