ISIL (Islamic State in Iraq and the Levant) has done some good. For example, it has ended the feud between Gulf oil state Qatar and the other Arab Gulf states over Qatar’s support for the Moslem Brotherhood. This is an Islamic radical group that has tried to play nice. It tried to do so in Egypt (where the group was founded before it spread all over the Middle East) and got the Moslem Brotherhood candidate elected president in 2012. But then, to appease its radical wing, the new Moslem Brotherhood government tried to impose strict Islamic lifestyle rules on Egypt. This angered the other Gulf states who saw the Moslem Brotherhood as an Islamic terrorist group with a moderate and democratic component that always lost out to their radicals in power struggles. The new policy also angered most Egyptians and by mid-2013 the Brotherhood was out of power. After that the radical fringe went to war with the rest of Egypt. This is what happened to the Moslem Brotherhood in the 1990s when its radical wing turned to terrorism and the backlash from the Egyptian government, and most Egyptians, greatly weakened the Moslem Brotherhood there.
Most Arab states also remember that Hamas started out as the Palestinian wing of the Moslem Brotherhood. Initially Hamas was largely a social service and political organization until it won an election in 2007 and gained control over Gaza. At that point the radicals took over and it’s been downhill for Hamas and Gaza ever since. Many Arabs no longer believe the Moslem Brotherhood can be trusted.
Qatar still believes in the Moslem Brotherhood but Saudi Arabia, the United Arab Emirates and Bahrain, which withdrew their ambassadors over the issue in March, are now joining with Qatar, and even that perennial enemy of the Arabs, Iran, to oppose ISIL. Qatari leaders still believe The Moslem Brotherhood is not a lost cause and that the dispute with its neighbors remains but will take a back seat until ISIL is dealt with.
All the Gulf states (Arabs and Iran) agree that extreme radical groups, especially one like ISIL that has declared itself the leader of the Islamic world (by declaring a caliphate run by ISIL) are the enemy of all Moslems. Actually, ISIL has a lot of supporters in all Moslem states, but these people are a minority (a few percent to maybe twenty or so in some countries) and most of these supporters would change their minds if they actually had to live under ISIL rule. That said, Saudi Arabia has long enforced strict Islamic lifestyle and beheads those who are major offenders of those rules. But the Saudis have courts and limits on the authority of those enforcing Islamic law. That makes a big difference, big enough to get a lot of Moslem countries that are at odds with each other over a wide variety of issues finally have one thing they can unite against.