BOG, people can use religion to justify conflict/murder.
Or they can use an atheistic ideology to justify conflict/murder. (See: the Soviet Union)
Or they can use economics to justify conflict. (see: Capitalism)
Whatever they use, you can also claim that blah... Is their God.
(like 'Money is their God', for Capitalist societies, or 'Communism is their God')
This doesn't make 'God' inherently evil, just because people are using it as an excuse to do evil things.
People fight for all kinds of reasons. Following Islam in Malaysia, Bangladesh, or Indonesia (three of the most populous states with Muslim majorities; 433 million people of which ~356 million are Muslim)is completely different from being from Nigeria, or Pakistan; from being Iranian (Persian) or Moroccan. (each country with a large Islamic population: ~364 million muslims)
The culture of East Asia is massively different from the Arabs Muslims in the middle east, or the sub-saharan Africans of Nigeria, or the Persian Muslims of Iran.
You can't simply lump them all into one category.
And even within the Arabs, there is a a huge variety of different school of thought, see: https://en.wikipedia.org/wiki/Islamic_schools_and_branches#/media/File:Islam_branches_and_schools.svg
There is one branch Wahhabism, which is considered ultra-conservative and orthodox.
To quote wikipedia "Critics say that Wahhabism's rigidity has led it to misinterpret and distort Islam, pointing to extremists such as Osama bin Laden's Al Qaeda network and the Taliban. The Islamic State of Iraq and the Levant (ISIL) also draws on Wahhabism for its ideology."
...and...
"The alliance between followers of ibn Abd al-Wahhab (1703–1792) and Muhammad bin Saud's successors (the House of Saud) proved to be rather durable."
You can see it is not an old tradition dating back to Muhammad (~610–632) but comes from over a thousand years later.
And you can also see that it is related to Saudi Arabia, which is the biggest US ally in the region.
Why? Because they have a lot of oil. (did i mention people will use economics as an excuse to violence? - there is a great quote from Noam Chomsky which i can't find right now, where he talks about US foreign policy in the 60s, where someone asks why people hate America, and is told, they hate us because we exploit their oil, and they should hate us for this, and we should take their oil this way... Basically the arguement that this is in the US national interest...)
So if you want to specifically discuss Wahhabism, and it's approximately 4.56 million followers in the Persian Gulf region. Then that is a very different discussion to have.
Or if you want to discuss why US policy, violence and oppression, lead to millions of deaths in the same region. Even why it might be in the US national interest. (Or what the Soviet Union would have done in the absence of US presence in the region... given that this directly relates to Russia [considered the successor state to the USSR], and now China getting involved in airstrikes against ISIS)
As i mentioned before, there is a geo-political game being played on at least three levels. The global one between Russia/China on one side, and the US/western allies on the other. The regional one between Iran and Saudi Arabia (with Turkey on the sidelines, while Egypt and Israel keeping well out of things) and the local one, where ISIS, the Kurds, and other local Shia/Sunni militias all fight for their own survival...
Without making any moral judgements, are these rational actors? Is this normal human behaviour, and tribalism? Can we expect better from international powers? Could regional powers push for a regional peace deal and carve up the region again (as it was carved up by the British/French when the Ottoman Empire collapsed?) These are all interesting questions - ones which i don't know how to answer.