Note, though, that I didn't say it doesn't have widespread acceptance, I said I wasn't willing to assume it did. Based on my personal experience (namely, more than a little with Muslims, albiet none with avowed Wahabbists), not one Muslim that I know advocates that specific interpretation of Islamic Law.
And looking at history, too...your best known (and hence presumably most active and supported) intra- and international Islamic terrorist groups weren't religiously motivated - they were either leftist or Arab nationalist organizations. The religion of Islam as a primary motivation for terrorism, as far as I can tell, first started in 1979 with the Iranian and Pakistani messes (Pakistani mobs sacked the American Embassy in Pakinstan in 1979 - apparently a little-known fact overshadowed by the Iranian hostage crisis), and only started to gain speed when the fall of the Soviet Union ultimately marginalized the leftist organizations and left a power vacuum for the fundamntalist organizations (i.e. al Qaeda) to fill. So why SHOULD al-Siba'i's interpretation be thought of as widely held, given that until relatively recently it wasn't even used as a justification?
Just my opinion (and analysis)...I could be wrong. But even if I am, I'm not as wrong as Rich.