The "radicals" you cite are from the 14th, 21st and 20th centuries. I would imagine that they go beyond the "extreme premises" of ibn Khaldun (whose work I know better), just as Pat Robertson or William Pierce go beyond the "extreme premises" of Machiavelli.
Yeah, and they are held up today in the islamic world as the great thinkers and intellectual anchors of "mainstream" islamic thought.
and I know that ibn Khaldun recognized non-Islamic governments as "legitimate", even if not to his ideal.
Incorrect. Khaldun recognized the ability of muslims to temporarily endure non-Islamic governments. He described the eventual overthrow of the Dar al Harb as a "religious duty" though, and wrote of the "universalism of the mission and (the obligation to) convert everybody to Islam either by persuasion or by force." (The Muqaddimah) He by no means saw non-Islamic government as something tolerable or on equal footing with Islamic government, and openly advocated the establishment of the latter where it did not already exist.
The "radicals" you cite are from the 14th, 21st and 20th centuries.
Very good. You've proven that you know how to google names! But what you've also inadvertently admitted is that the intellectual strain of islamic radicalism runs very deep through Islamic history - in fact it follows a succession over 600 years in the making.
I would imagine that they go beyond the "extreme premises" of ibn Khaldun (whose work I know better)
May I take it by your scare quotes that you question whether Khaldun's advocacy of forceful conversion to Islam is indeed an extreme premise?
just as Pat Robertson or William Pierce go beyond the "extreme premises" of Machiavelli.
Your analogy is false. Pierce was a fringe writer with no significant or credible following in the western world. Taymiyya, Qutb, Sadr, Mawdudi, Wahhab, and other jihadi radicals all have significant followings among Islamic theologians, political figures, and, of course, terrorists.
The Robertson analogy is similarly false, as Robertson and his followers don't blow up busses, ambush conveys, or take and execute hostages. Sadr does. So did the terror cells spawned by Qutb and Mawduddi.