No; that’s exactly the point. People like Holocaust deniers are diseased — mentally diseased, but diseased nonetheless. Their hatred is communicable to similarly predisposed individuals via the “vector” of lying. In such cases where physical disease can be communicated between people, we can and do go to substantial lengths to prevent the spread of the disease. We must do similarly with this other kind of disease. One way is to stop the intentional spread of lies. Lies undermine rational decision-making and societal well-being generally.
In this case, most Western Holocaust deniers have had the opportunity, ability, and means to learn the truth. They have absolutely no justification in spreading those lies. They are denying truth in spite of overwhelming evidence. That’s the definition of delusion. They must be treated as dangerous mentally ill persons if we are to ever have a truly successful society.