The author is probably right that Al Qaida leaders appreciate the psychological effect of recruiting doctors to be terrorists, but I suspect that the recruiters have a more practical reason for choosing doctors. Because doctors' services are in high demand, they are able to immigrate to western countries much faster than, say, a taxi driver. In conducting a terrorist operation in a foregn country, getting your operatives where they need to be at the time you need them is paramount. Al Qaida leaders might want any number of types of persons to plant the bomb, but their choices were limited to those who could get a work visa.