Irving is always described as a historian but in the potted biographies I have seen (not many admittedly) I haven't seen any academic qualifications.

There seem to be two questions here. Is the Austrian law right and should Irving have been jailed under it. As some have posted above if you go to a country, break the law quite publicly and then return you can expect what you get. I think that Irving uses Holocaust denial as a way of taunting Jews and I think that is unacceptable. Not being an Austrian I can't really appreciate how important or not this law is to them but it must make it more difficult to be a Nazi in Austria and that is no bad thing. I think repeating racist lies reinforces them.