Why should Holocaust denial be a crime?

Re: Why should Holocaust denial be a crime?

No one denies that millions of Native Americans were killed by whites or that millions of blacks were killed either. No one denies the killings in Vietnam.
Denial seems to be a Muslim trait. How many millions were killed in Bengal? How many are being killed in Sudan? Nigeria? East Timor? Why are there only 3% Christians in the Arab world when there were more than 25% in the 60's?