Actually, she did say that dogmatism ONLY comes from either end of a spectrum.
In this context "can" denotes the ability to do something (e.g., "can come from either end of a spectrum"), so it is assumed that any alternative denotes "can not," (e.g., "can not come from either end of a spectrum"). Thus what she said, in essence was, "... dogmatism ONLY comes from either end of a spectrum."
Were she merely denoting a possibility out of several alternatives (e.g., "either end of a spectrum is possible, but so is somewhere in between"), as you are suggesting, she, being well bred and educated, would have used "may" or "might," both of which indicate possibility rather than ability.
But grammar aside, parsing her statement the way you suggest, reduces it to meaninglessness. In that case all she was saying was that there was a possibility of coming from anywhere at all (e.g., no where in particular) a concept that leaves her entire paragraph with neither meaning nor significance.