You may be interested in our FAQ section on Holocaust Denial.

I like Ike, so I'd just quote him on the topic and leave it at that. In a letter to George Marshall in April of '45, Eisenhower said:

"But the most interesting -- although horrible -- sight that I encountered during the trip was a visit to a German internment camp near Gotha. The things I saw beggar description. While I was touring the camp I encountered three men who had been inmates and by one ruse or another had made their escape. I interviewed them through an interpreter. The visual evidence and the verbal testimony of starvation, cruelty and bestiality were so overpowering as to leave me a bit sick. In one room, where they [there] were piled up twenty or thirty naked men, killed by starvation, George Patton would not even enter. He said he would get sick if he did so. I made the visit deliberately, in order to be in position to give first-hand evidence of these things if ever, in the future, there develops a tendency to charge these allegations merely to 'propaganda'."

I've spent time arguing with creationists, way too much time. I'll argue with 9/11 Truthers. I draw the line at Holocaust Deniers. Evidence is not the issue and they generally don't actually deny that the Holocaust occurred. They really want to say how evil the Jews are and how much the Jews deserved it.