First of all, this is NOT the position of the vast majority of atheists.The Atheist's Manifesto
"We take the side of science in spite of the patent absurdidy of some of its constructs, in spite of its failure to fulfill many of its extravangant promises of health and life, in spite of the tolerance of the scientific community for unsubstatiated just-so stories, because we have a prior commitment, a commitment to materialism. It's not that the methods and institutions of science somehow compel us to accept a material explanation of the phenomenal world, but on the contrary, that we are forced by our a priori adherence to material causes to create an apparatus of investigation and a set of concepts that produce material explanations, no matter how counterintuitive, no matter how mystifying to the unitiated. Moreover, that Materialism is absolute, for we cannot allow a Divine Foot in the door." - Carl Sagan
Second, it was NOT a quote of Carl Sagan. it is a quote from Richard Lewontin who was reviewing a book of Sagan's.
Third, if you can find a way to test the 'non-material', I'm sure there are many scientists who would be willing to theorize, test, and figure out how it works. The rule of science isn't some fuzzy materialism, but the simple idea that ideas must be testable and that general principles must stand up to tests designed to show them wrong.
Finally, Dr. Lewontin is not a spokesman for ALL atheists or even all scientists. Lewontin was a marxist, with very particular views (which were often wrong).