To Reefer and Keyplus -
“I think the argument people have is about the figure of 6 million not that people were gassed and killed in camps.”
Various historians have given estimates from anywhere between 5.1 and 6.3 million Jews killed. He's an example of such as estimate -
From the 'Encyclopedia of the Holocaust” (published 1990, page 1799) - Estimated loss of Jews in the Holocaust:
Total number before: 9,796,840
Minimum after: 5,596,029
Maximum after: 5,860,129
The above figures are not pulled out of thin air. They were compiled by a number of scholars each working in his or her own geographic area of speciality and then combined by Yisrael Gutman and Robert Rozett. The figures were taken from 21 countries and were derived from population demographics, taking the number of Jews registered living in every village, town and city in Europe, the number of reported transported to camps, the number liberated from camps, the number killed in 'special actions' by the Einsatzgruppen, and the number remaining alive after the war. The minimum and maximum loss figures represent the range or error variation.