That may turn off the American listening public, but I really don't think that idea would hinder his ability to recruit in the least. What he's appealing to is emotional, not rational, and if he's a good speaker the idea could easily backfire.

There are a number of historical examples to back this up, but I'd like to look quickly at just two. The first are the European terrorist groups of the 1970s and 1980s (some of which still exist today). How many Germans really believed that the Red Army Faction wanted to "free" the workers? Or how many Italians thought the Italian Red Brigades had the same goal? Not that many in real terms. But they both could tap into just enough resentment, idealism, and urges to destroy the "system" that they managed to keep a flow of recruits coming. The second example is Hitler. I'm not saying Bin Laden is "evil" in the same sense, but many in Germany (and the rest of the world) figured that his message was too nonsensical to be believed. It was, but he was also a hell of a speaker and audience manipulator. By the time some folks figured that out, it was too late.

Messages can be tailored. Hitler understood this, as did Stalin, Castro, Ho Chi Minh, and other revolutionary leaders. They also understand that just because we (and I use the term in a very generic sense) think their message is absurd doesn't mean that others will feel the same way. And if they can win over a few of the others they come out ahead.