How to reference a website article of discussion between two people, posted by a third?
I would include as much bibliographic information as possible, but as long as the reader can unambiguously find the article I think that would suffice, and to find the article you need the author.

In your bibliography:


  Gooch, J (2013) Point-Counterpoint: Additive vs. Subtractive Rapid Prototyping. Webpage: http://www.rapidreadytech.com/2013/09/point-counterpoint-additive-vs-subtractive-rapid-prototyping/ [URL accessed: April 2015].


In your text you could use something like:


  Grimm, in Gooch (2013), states...