Many Sunni neighbours joined with the Islamic State in attacking Yazidis

The Yazidis had long been subject to persecution before the Islamic State seized one of the main towns Sinjar and villages in the area. Sunni Arab neighbours and Kurds considered them "devil worshipers."

Their reputation as devil worshipers comes from the fact that another name for one of the archangels that the group worship Tawuse Melek, is also the name for Satan. However, the Yazidis do not consider this archangel a source of evil: For the Yazidis: "They also hold that the source of evil is in the heart and spirit of humans themselves, not in Tawûsê Melek." As far back as 2007 Yazidis were the subject of murderous attacks:

   In August 2007, some 500 Yazidis were killed in a coordinated series of bombings in Qahtaniya that became the deadliest suicide attack since the Iraq War began. In August 2009, at least 20 people were killed and 30 wounded in a double suicide bombing in northern Iraq, an Iraqi Interior Ministry official said. Two suicide bombers with explosive vests carried out the attack at a cafe in Sinjar, a town west of Mosul. In Sinjar, many townspeople are members of the Yazidi minority. 

 When the Islamic State recently invaded Yazidi-populated areas, many of their neighbors actually helped the Islamic State and supported their attacks against the Yazidis. A few individual examples are detailed in this New York Times article:

The afternoon before his family fled the onslaught of Sunni militants, Dakhil Habash was visited by three of his Arab neighbors. Over tea, his trusted friend Matlul Mare told him not to worry about the advancing fighters and that no harm would come to him or his Yazidi people. 

 The two neighbors had helped each other for years. However, Habash had doubts and fled with his family that night. Later he found out his neighbour had actually joined the Islamic State and helped them hunt down Yazidi families. Habash said: “Our Arab neighbors turned on all of us. We feel betrayed. They were our friends.” Another Yazidi said that before the IS entered his village, Arab neighbours flew their black flag. Not all their Arab neighbors joined in the Islamic State oppression — some actually helped Yazidis escape at great personal risk to themselves.

 This was the case even with Mr. Habash: Though Mohsin Habash’s family suffered because of one Arab neighbor, he pointed out that they were saved with the help of another: a longtime friend who led a convoy of Yazidi refugees to safety at great risk.The convoy drove through the night, passing ISIS-controlled territories undetected. Mohsin Habash believes it was because his friend knew the Arab areas better than any of the Yazidis. Hours later, they reached Syria. From there, Mohsin Habash’s friend introduced them to another Arab man who took the group the rest of the way to the border with Kurdistan.  

There are cases where friendship triumphed over religious differences but more often if would seem the opposite happened.