[y4mi]

At least the wikipedia articles seems to agree with the author.

  These cities continued to be used by the Christian natives 
  as protection from the Mongolian incursions of Timur in 
  the 14th century.[7][8]

  After the region fell to the Ottomans, the cities were used 
  as refuges (Cappadocian Greek: καταφύγια) from the Turkish
  Muslim rulers.[9] As late as the 20th century the locals, 
  called Cappadocian Greeks, were still using the underground
  cities to escape periodic waves of Ottoman persecution.[9]
  R. M. Dawkins, a Cambridge linguist who conducted research
  on the Cappodocian Greek natives in the area from 1909-1911, 
  recorded that in 1909, "when the news came of the recent 
  massacres at Adana, a great part of the population at Axo took
  refuge in these underground chambers, and for some nights did 
  not venture to sleep above ground."

[delidumrul]

Many books are written to shape the history in the benefits of some countries. Linking them with other topics will attract more attention and will help to exaggerate effects of their claims. The passage above from wikipedia is a nice example of this propaganda technique. Underground cities are associated with totally another political issue. The blog post, the situation is just inflated and dramatized more: domino effect. It would be too long and unnecessary to answer all accusations, though. Here is not a place for historical or political discussions. Therefore, to sum up, as a local of Cappadocia, I can say that these places are not really unknown places. In this area, there are many underground cities inside the villages (since at least 1900s), not in isolated places. People used these places as warehouses. If a crime existed, then people could have been found there at most as hardly as in a normal village. Hiding on mountains would be a more plausible option. In the early centuries, against invasions, it may be safer than a regular village, because they are generally inside valleys and not in a place where a popular road passes. So, it can't be discovered from far points by eyes.

There are many churches in caves or as buildings. The ones as buildings are from 1800s. Ones in the caves are more older apparently. Also, many historical Greek houses exist. Majority of them contains caves as parts.