This is an interesting question. There are several possible explanations, which may overlap in an individual.
1. There are people who get a kick out of being different and/or outrageous or defying what they see as 'political correctness'.
2. They want notoriety.
3. They want to find an outwardly 'scholarly-looking' excuse for Jew-baiting.
4. In some Islamic countries, there is a feeling that Israelis (and many Jews elsewhere) use the Holocaust as an excuse for maximizing their position. So, in some countries in the Middle East holocaust denial is widespread.
Obviously, one can only guess. Some obvious motives include:
When 5-star general Dwight D. Eisenhower witnessed the liberation of Ohrdruf concentration camp, he knew people would deny it and he wanted the entire camp filmed. Today, there are some people who deny the Holocaust; all of them are anti-Semitic and hate Jews for one reason or another.
Please have a look at the related question below, which may answer your question.
he knew it happened
A historically false claim, it is not necessarily Iran, but their leaders who deny the Holocaust. They do this a part of a series of other absurd claims in order to justify destroying Israel.
Many Muslim countries do not recognize Israel.Some Arabs and some other Muslims believe that the Holocaust is misused to enhance the legitimacy of Israel.Many go a stage further and find it convenient to deny the Holocaust altogether.
Of course it's not illegal in the US. There are 15 or 16 countries in Europe where it is illegal to deny the Holocaust in public.
"The American Historical Association Council strongly deplores the publicly reported attempts to deny the fact of the Holocaust. No serious historian questions that the Holocaust took place." See link for reference and for background.
The Holocaust did not and could not attack people.
Yes it is, as well as 12 other countries. (Note that this relates to public denial).
No one fought in the holocaust. People died in the holocaust. People killed people in the holocaust. There was no fighting by men or women....but jsut because there was no fighting, don't think it was peaceful.
the outcast of the holocaust was that millions people were killed and thousand of people was traumatised
People deny lying because they want to find a way out of it.