They probably knew his anti-imperial motives pretty well, his tendency to violence, his desire to rid the Middle East of first-world influences. Just like they knew Saddam was a thug when the USA armed him to fight Iran.
At some point Muslims probably realized the US was helping them play "let's you and him fight." Then again, some seem to have no qualms about killing their religious fellows (Muslims killing Muslims.)
Yup. They sure did good to just walk away from Afghanistan after the Soviets withdrew. With all those jihadists in one place, what could go wrong?