The fact that Jews were targeted and killed is not denied by (almost) anyone. The question that the Iranian president is referring to is, how many and under what circumstances. There are serious questions about the numbers of those killed and under what circumstances. Why is it illegal to examine these issues?
[...]
the issue of the holocaust and questions about it are not solely the province of nuts, anti-Semites and hate mongers.
Soj at BooTrib
Soj's remarks illustrate a common misunderstanding of Europe's laws against Holocaust denial. In reality, raising serious questions, examining the issues relating to the Holocaust is not illegal. On the contrary, it is a thriving academic subdiscipline with many articles and books being released each year. What is illegal is denying the basic facts, and the only ones who risk prosecution are racists. Let me explain, starting with what is and what isn't a matter of debate, and from there go on to the question of Holocaust denial.