You misread the guys post. I'm fully in favor of stating this man is as stupid as Pat Buchanan for engaging in holocaust denial
He said he is as stupid as Pat[insert break] for his[Austrian guy's] activity i.e holocaust denial. He isn't saying Pat has engaged in that actvity.
Rules of grammar and logic dictate to me that the dependent clause (for engaging in holocaust) applies to Pat Buchanan, against whom "this man" is being compared.
Best bet is to say ".... this man who engaged in Holocaust denial is as stupid as Pat buchanan....". that way it will be clear what is being said.
Remember, Pat was accused of being an anti-semite or a fascist sympathizer for two things ~ one of which was for alleged "softness" on neo-Nazis, and for supporting one side in a trial of a guy accused of having been a deathcamp guard. (Turned out guy had been a guard, but not the one some witnesses said he was). Because of this you really have to be careful how you refer to Pat in threads like this one because you will be asked for references to any item for which he was not previously accused.