Mining operations for example in the Roman times were hardly any different, thousands if not more died in equally horrible conditions. The construction of the buildings and the mechanim may have changed but the results were the same.
And I don't want to poorly paraphrase Aimé Cesaire, so I'm taking a translated quote: 'What he cannot forgive Hitler for is not crime in itself, the crime against man, it is not the humiliation of man as such, it is the crime against the white man, the humiliation of the white man, and the fact that he applied to Europe colonialist procedures which until then had been reserved exclusively for the Arabs of Algeria, the coolies of India, and the blacks of Africa.'