Cossack
If I know there to be something on the runway which may cause, however unlikely, an incident, it is in my duty of care to not let you use the runway.
One could argue that an alternative approach would be to advise the Pilot-in-Command that, for example, a dead small bird is on the runway centreline 500 metres from the threshold, and ask for his intentions with his aircraft.
That would CYA whilst providing the Captain with timely and useful information from which the best decision could be made.
Clearly if the obstruction is a dead cow/vehicle on runway it is a different matter.