Look at this very article. If he weren't in jail, would Irving have such a lofty perch from which to preach? I suppose Canadians and Europeans are more authoritarian than Americans and are more likely to see imprisonment as a natural discreditation of ideas, but if one agrees with the idea, then imprisonment tends to reinforce the validity idea. See Nelson Mandela.
Irving is just mad that he couldn't get a furlough to go to Tehran.
I look at the neo nazi types in europe as an example of why attempts to silence idiots doesn't work. Sure we have neo nazis in this country but they seldom become violent. In europe, the illegal groups still exist and when we hear about them it's usually due to a violent act that gets the news.