As you clarified, it's not an opinion. Irving is spouting blatant lies. Mentally ill nut jobs spouting similar incoherent nonsense have been arrested and ultimately committed to psych wards after being swept off city streets.
I would tend to agree with you in the end, but this is pretty damned close to shouting "fire".
Understandably, it crosses the line in Austria and Germany.
Lying is legal, though one could always be sued for damages.
(One can also be so sued for telling the truth...)
I agree that doing it in Austria is different from doing it in England, because presumably some group of Austrians must have invited him to speak.
But see my post above. I don't think we disagree about Irving, we just disagree on what the most prudent way of dealing with it is.
How Austrians deal with hate crimes (a dubious category but perhaps sometimes justified) is their business. But since Irving evidently hasn't spread his lies there for 16 years, this prosecution doesn't strike me as an imminent necessity to prevent the spread of Naziism.