Scientism is simply not a coherent position. You cannot avoid having distinctively philosophical and extra-scientific theoretical commitments, because the very attempt to do so entails having distinctively philosophical and extra-scientific theoretical commitments. And if you think that these commitments are rationally justifiable ones – and of course, anyone beholden to scientism thinks his view is paradigmatically rational – then you are implicitly admitting that there can be such a thing as a rationally justifiablethesis which is not a scientific thesis. Which is, of course, what scientism denies. Thus scientism is unavoidably self-defeating.