There is no rational justification for Holocaust denial.

In places such as Germany and Israel, Holocaust Denial is illegal.

Please See Related Links below.

Holocaust denial is most active in United States, because of freedom of speech (First Amendment)

Despite what people may think, Holocaust denial and swastikas are illegal in Germany and those who disobey this law are often fined and temporarily imprisoned.

Denial - outright rejection. --- Note that denial is also used in the sense of dogmatic refusal to believe (something). Well known examples include Holocaust denial and climate change denial.

unquestionably!