Via Yglesias, we see the perfect example of why from the conservative National Review:
The problem, as I see it with using the term “Bin Ladenism": It can’t be applied to the ideologies of the ruling Iranian mullahs, Saddam Hussein loyalists or other Baathists (e.g. in Syria).
Bin Ladenists are engaged in a rivalry with Khomeniists for leadership of the international, radical Jihadi movement. Baathism (pan-Arabism and Arab supremacism) is largely a spent force but its remnants have merged both with bin Ladenism (e.g. in the 1990s, Saddam “got religion”; “secular” Fatah has produced the al-Aksa Martyrs Brigades and reveres both Saddam and bin Laden), and with Khomeinism (the Damascus – Tehran axis).
We are struggling to come up with a term that (1) accurately describes the network of ideologies and movements that have risen up with the “Muslim world” (I hate that phrase) and which seek to defeat America and its allies, a term which also (2) clearly conveys to the average person in the West that this is an enemy who must be taken seriously.
That's a real puzzle, isn't it? You have a bunch of separate groups with a bunch of separate goals, who each hate us for separate reasons and which pose varying threats to us. They aren’t united and many have a history of direct conflict with each other.
Granted, there are common threads. They all oppose us to varying degrees and for varying reasons that mostly all go back to 1. Our support of Israel, 2. Our quest for cheap reliable oil.
Those who are unable to see the distinction between these groups put the US at a strategic disadvantage. Though they think of themselves as clear-eyed defenders of us all they should remember that Neville Chamberlain did to.