There is a book entitled, "New Martyrs of the Turkish Yoke," which is the Lives of the Saints who were matyred by the Ottoman Turks-Muslims-during the years they ruled parts of Eastern Europe, and probably before. Most of these Lives were written close ot the itmes of these martyrdoms, and gove quite a few details of the way the Turks martyred these Orthodox Christians who refused to abandon their Orthodox Faith and embrace the false religin of Islam. These Muslims killed many, many, many Orthodox Christians, and they used extremely gruesome and brutal methods to do so. This may have a lot to do with the "negtivity" held by Orthodox Christians towards Muslims. Also, many Orthodox Greeks were killed by the Muslim Turks in the Greek-Turkish War of the early 1920's-many people still alive in Greece had relatives killed. And, I believe, there have been Muslim terrorist attacks in Greece throughout the past several years. All this, added to the current climate of Muslim terrorism against Christians in general, I believe, wold explain the "negativism," as you call it.
Also, the oft heard cliche that "Islam is the Religion of Peace" is not exactly what I would call the truth...Islam was the religion of the sword par excellence at the time of its origins...North Africa wasn't converted to Islam by peaceable young men in bowties knocking on people's doors selling the "Islamic News!"