Extremist can here refer to radio talkers and politicians of relatively mainstream Democratic or Republican instincts, to judge from the commentary about what the government has chosen to make available. The article might have Islamist true believers in mind, for whom the absence of evidence is not evidence of absence.
It helps to understand that sometimes the simplest explanation is the most compelling.
Attitudes and perspectives ought to be receptive to logic and content. It does no good to complain that rules of logic or of evidence privilege some perspectives over others. Deconstruct that.