Do you agree or disagree with the following premise: "As societies move away from organized religion into less structured beliefs systems, extremism will be less common and there will be fewer civil and international conflicts"?Clearly define and defend your argument.

An interesting question. I would lean heavily towards disagreement with the statement. You should of course make up your own mind on the subject, as it asks whether you agree or disagree on a personal level, but here are some points to consider in terms of approaching and structuring your answer.
First, the question asks you to consider the impact of organized religion upon two separate things: extremism and civil/international conflicts. These are discrete issues, so we need to tackle them separately.
Looking at the idea of extremism first:
1. Is the majority of extremist terrorism caused by religion? Today, there is certainly a pressing threat from ISIS. In the past, there have also been significant terrorist threats based on Christian religious differences, such as during the era of the Troubles in Ireland, which led to car-bombing and terrorist attacks by the IRA. So, religious extremism certainly causes some terrorism, and in the Irish arena, it was organized religion specifically that caused this. However, Islamic terrorism is not engineered by those adhering to the organized religion. Islamic terrorism is driven by extremist fringes who are actually acting in opposition to the teachings of their religion, much as Christian extremists who bomb abortion clinics do not act in accordance with the teachings of organized Christianity.
2. Is most terrorism caused by religious extremists? Since Trump took office, more domestic terrorism in the US has been carried out by white men with no religious affiliation at all. These men have generally been driven by issues such as social division, which has led to fascist sympathies, and have disturbing connections to such theories as "InCel." "InCel," or unwillingly celibate men, is a group that organizes on the internet and unites frustrated young men, providing a platform to drive their hatred of women and sense of entitlement. As such, we might question whether banning religion would simply drive people to seek a sense of purpose elsewhere, encouraging this sort of congregation.
3. Always remember that Nazi Germany, the twentieth-century's greatest example of national extremism, saw the Church as a threat to its power and sought to stamp it out. It was in the absence of open, organized religion that fascist extremism rose to its greatest heights.
Ultimately, extremism is driven not by religion—although religion may play a part—but by prejudice, which may be based on a multitude of things. Some organized religions even serve to dissuade people from this kind of prejudice and provide assistance following extremist attacks. As such, we would need to tackle the social inequality which leads to prejudice in order to minimize extremist terrorism, rather than hoping organized religion dying out would put an end to it.
Secondly, let's look at the issue of civil and international conflicts, which is a simpler question to answer.
1. Religion does drive civil conflicts (as in Ireland and the Middle East).
2. Religion is not the cause of "most wars," by a long stretch. In the "Encyclopedia of Wars," by Phillips and Axelrood, 1,763 wars are listed, of which only 123 (7%) were driven by religion.
As such, it seems fairly safe to say that the death of organized religion would not have a significant effect on the amount of wars fought worldwide.
https://www.bbc.co.uk/news/world-us-canada-43883052

https://www.huffpost.com/entry/is-religion-the-cause-of-_b_1400766