The flood that produced the scablands is well understood, and has a perfectly natural origin. It is not evidence for the existence of an advanced civilisation. But civilisations do always leave evidence of their existence - heaps of it - and this is not to be found. Pyramids are evidence of social organisation, not of advanced technology.Are microspherials negative evidence?
Are the scablands negative evidence?
Maybe you could give me another example negative evidence, and how that squares with Shermer saying someone is well researched and well reasoned?
Scablands are evidence for end-ice-age floods, when meltwater was suddenly released in huge volume by the thawing of permafrost features that were previously holding back lakes.