It might be difficult to find any people willing to admit they support him to ask.
When dealing with quasi-religious fanatics its not really a valid question. The response will almost certainly be something along the lines of "all things are justified if done in the name of allah/buddha/jahweh/adam smith/you name it". Sad, but true. Generally takes religions about 500 years to grow out of this sort of behaviour.....lets hope we live that long.
As far as I know, he hasn't claimed that the Anthrax attacks have anything to do with him. As for how you justify it, he'd probably say it was the only means he has to attack America since he lacks the men and/or weapons to attack directly.