Why is this crime worse than any other?
I presume you mean any other triple homicide, in which case it isn't. The hatred of the killer, particularly organized hatred, is a separate issue. Despicable, worth of condemnation, but as Dershowitz notes, in America, not an issue for prosecution. And hate crime laws make speech a crime. I do think it's a legitimate sentencing issue, but not formally.
In other words, even in America, with its extraordinary protection for free speech and freedom of conscience you can be prosecuted for your ideas and beliefs. No matter how odious or unpopular those ideas and beliefs may be, it is unjust for courts to pass judgment on them.