The Destruction of the Inscription - Motivations?

I am tempted to refer to the Inscription as one of the wonders of the late antique world but clearly from the lack of reference to it by anyone in the ancient world, it was not exactly a "must see" on the path of ancient world globetrotters. Still it seems a prodigious work looking back over the intervening millennia. We have no records of any other inscription in stone that was so voluminous. As a work in stone, non-sculptural, the only other major work we can think of is the enormous map of ancient Rome (the Forma Urbis) which adorned the walls of the Temple of Peace in Rome.   

So if Diogenes' inscription was scarcely a tourist draw then seemingly the Oinoandans must have become blasé about this enormous diatribe that they passed on a daily basis as they scurried about doing their shopping and other business in the "upper" agora. We all know the sensation of the "same old, same old".

We don't really know how the ancients felt about the works of art that were around them. Certainly the inscription would have been familiar, something that had always been there, and as we know familiarity breeds contempt.

So at some stage the contempt or disinterest reached a point at which the inscription did not have enough advocates to resist its destruction. Whether this destruction was an expedient to gain building materials after the town had retreated to the other side of the Great Wall or whether a religiously inspired claque decided to expunge a competing "lifestyle option" from public view is unknown and may never be known. What is clear is that it was not demolished solely to build the wall (if that indeed was the reason) for while some pieces were embedded in the wall the vast bulk ended up scattered over a very wide area. In fact their distribution looks more like the debris field from an explosion rather than a focussed reusing of spolia.  

It may very well be that the stoa with the inscription was looked at for its building material value more than anything else. However, it merits looking at the views of the early Christians towards Epicurianism to see whether there was something in the inscription that caused it to be dismembered so completely. 

While Epicurianism had its scientific elements which did not clash with Christianity (which at an early date did not come freighted with dedicated flat-earthism) it had enough in ideas of ethics and views on the afterlife (or lack thereof) which made it potentially an annoyance to the burgeoning Christianity of Constantinian times. The history of disputations is long with Christians on the State-sanctioned high ground. The target was the specifically Epicurean denial of divine providence and after-life and affirmation of pleasure as the supreme good and of materialistic atomism.  

The main website on Epicurianism gives a comprehensive survey of attacks by the Early Fathers and their literary camp followers. We shall not reiterate all this except to quote: "By the mid-2nd century A.D., the Christian movement had become secure enough so that it could aspire to win converts from more educated circles. Certain church leaders began to seriously engage themselves intellectually against Greek philosophy, often in the form of written apologias against “pagans” and rival Christians. These works routinely included attacks on Epicureanism, as shown by Tatian's Address to the Greeks, Justin the Martyr's Hortatory Address to the Greeks and On the Resurrection, and Irenaeus of Lyon's Against the Heretics.

Two significant anti-Epicurean themes emerged in these early apologias: first, Justin and Tatian mocked Greek philosophers as being hopelessly disputatious with one another, taking their disagreements as evidence that human intellect could not arrive at definite conclusions about reality (a somewhat ironic charge in view of the emerging factionalism of the Christians themselves)".

Tertullian then moved in for the attack and several decades later, Origen wrote Contra Celsum in reply to Celsus (who had Epicurian leanings), and Lactantius included lengthy arguments specifically against Epicureanism in The Divine Institutes. With Lactantius it became manifest that Christians were no longer content to argue for their position on the grounds of faith alone, but were beginning to embrace Platonic arguments in favor of divine providence, accusing Epicurus of falsehood in not recognizing the role of divine intelligence in ordering the cosmos; and also Platonist criticisms of Epicurus's ethics. 

With this mood in general circulation (and official favour) it would have been fairly easy to have declared the Inscription as anathema for either philosophical or building material needs and do the deed of destroying the work of Diogenes.