There are no easy answers here. I prefer not to be so gauche as to link my own essay, but this case touches on so many points I would essentially have to reproduce the whole essay here to address them all. 
 What I can say for certain is it should not be the intention or expectation of editors to prove that Bateman is right or wrong. It's my assessment (though still up for debate), that his book is not self-published, and there cannot be a blanket statement that his views are WP:FRINGE. Some of his specific views may be fringe. He represents a significant viewpoint, which there is a duty to cover under WP:NPOV. He is definitely biased. If a point can be made using better sources, that should be preferred. Contradictions between sources should be highlighted, rather than used to suppress a source. Don't explain a contradiction unless a source explains it.