Some will be swift to point the finger at Islam as a whole for being responsible for Masood's actions, a view that is not only deeply misguided, but runs the risk of feeding the narrative of the very extremists we are seeking to defeat.
Islamism, or, again, political Islam, is a far cry from the religion that is familiar to the 1.7 billion Muslims around the world.
The wayward application of the terms Islamic and Islamist muddy the water and do not help separate two entirely divergent strands of thinking.
For the overwhelming majority of the world's Muslims -- both converts and those born in Islam -- it is a faith that stresses the importance of personal piety and purification, for striving to uphold peace, justice, and social equality.
For Islamists, however, Islam is not simply a matter of faith, but rather a political ideology that must be instituted regardless of people's wishes, sometimes with the use of force.
But the question remains: why do individuals follow this ideology?
Those who buy into this worldview are often lured by the simple narrative that is spun by Islamists, providing simple answers to address the complexities of the increasingly globalized world we live in.
Their literalist worldview divides the world into black and white, right and wrong, believers and non-believers.
Islamists seek to tarnish all those who do not subscribe to their narrow interpretation of Islam as deviants, and in some cases declaring them as apostates -- an accusation that often comes with the threat of death.
There have been elements of extremists on the fringes of Islam since the earliest days of the faith. They have always been considered to be extreme, misguided, and fundamentally wrong in their approach to the faith, but their military defeat came after a religiously rooted engagement with their ideas from the leaders of the Muslim community.
The Khawarij -- a group of deviants that emerged in the first century of Islam
-- sought, just as the extremists today, to apply Islamic scripture in a literalist manner without context, and designated those Muslims who opposed them as disbelievers.
Ibn Abbas, who was not only a relative of the Prophet Muhammad's, but one of the earliest authorities on the Quran, systematically engaged and dismantled the group's misguided ideas about the religion, which according to Islamic sources, led to 2,000 of these renegades accepting their mistakes and returning to the mainstream.
Islamist extremists are the same today. They are narrow-minded, fundamentalists with a warped worldview and a perverted interpretation of scripture that represent nothing but a fringe of the world's Muslims.
For those of us who strive to uphold the values of liberal democracy, challenging and questioning ideas makes for an uncomfortable conversation. But we have to accept that Islamism is a set of ideas, and the violence is a symptom of those ideas.
Converts are vulnerable to these ideas. Often isolated in their new communities, extremist groups know to exploit that isolation, offering them an anchor.
They have not grown up imbued with the Islamic tradition or teachings and are therefore easily swayed by Islamist ideology. In a lot of cases, troubled by sins of their previous existence, they will seek to atone through zealotry.
Islam, like Christianity, is a proselytizing religion. But the mainstream has a duty to converts: let them gain their sense of meaning in the central current of the religion, imbued in its traditions and beauties. Don't allow them to be captured by extremists, seeking to exploit them for their own ends.
As a Briton, a Londoner, and a Muslim, I would urge Western policymakers and the public not to succumb to the division that extremists are striving to sow. Our struggle must be against those -- and only those -- who seek to misrepresent the faith of Islam as a fundamentalist, fascist ideology to spread hate and division.
These ideas and the violence do not recognize boundaries or borders. They do not discriminate between Muslim and non-Muslim. They cannot be defeated by military means alone.
Engagement not only with our Muslim allies around the world fighting ISIS, but with the Muslims that live in our very own countries, is integral to our success.
Building a coalition of those willing to strike at the heart of Islamism will destroy its ideas.