The question is this: If you could magically turn back time to prevent the exploitation of hundreds of thousands of human beings, would you? If you count yourself among the functioning population in a civil society, the answer is an easy "Yes."
Why, then, do I hesitate when the result of that exploitation happens to be the Great Pyramids of Egypt? Is the mass exploitation of humanity justified if the end result is a Wonder of the World?
Perhaps it is that we are so many millenia removed from the suffering of those ancient people that it no longer repulses us in the same way. Is there an experation date on suffering - some moment in time when reprehensible means are overlooked by the magnificent ends?
The suffering of the movers of those great stones are as ephemeral as their tradgically short lives, leaving only the ends of their labor to judge.