What Is the Key Point That People Should Know About the Holocaust?

1) That Jews were terribly, horrendously persecuted and killed?
2) That there was an orchestrated, state-run genocidal campaign against Jews?
3) That 6 million Jews were killed by the Nazis?
4) That gas chambers, specifically, were used to kill millions of Jews?

I don't think any one denies the first point. The persecution was obviously terrible, and incredible numbers of Jews clearly died as a result.

The second point is obviously an important historical point, and certainly believable. My understanding is that there is a little room for debate here, but raising this issue gets you called a holocaust denier.

The third point is obviously only an estimation. But if you question this number, you tend to get called a holocaust denier.

The fourth point doesn't seem to as critical, conceptually, as the other three points, although it does tie into point 2 fairly closely. If you question the gas chambers, you definitely get called a holocaust denier.

This section from wikipedia on holocaust denial is interesting:
According to James Najarian, Holocaust deniers working for the Institute for Historical review are not trained in history and "put out sham scholarly articles in the mock-academic publication, the Journal of Historical Review".[152] They appeal to “our objectivity, our sense of fair play, and our distrust of figurative language”.[153] Thus, they rely on facts to grab the readers’ attention. These facts, however, are strung by what Narjarian calls “fabricated decorum” and are re-interpreted for their use. For example, they pay particular attention to inconsistencies in numbers.[154]
Emphasis added.