I think the real evil is the guy who goes about convincing others that this is a Holy War that God wants.
I concur. The 'others' in this case are vulnerable marginalised people. They become susceptible because of their situation. Often poor, poorly educated, and unemployed without a future, they'll be far more easily convinced. The techniques used are little different than predatory evangelism in impoverished nations with the promise of a better future. In evangelism, the goal is religious conversion, but in this case it's more a political conversion, an ISIS friendship.
So we have to look deeper. The Sri Lankan government needs to look much deeper, stop scapegoating the minorities, and ask themselves the tough question of why these minorities are so upset that they'll take to 'terrorist' activities to make a statement. Unfortunately that backfires, and the people just make it worse for everyone. When young men face discrimination and harassment on a daily basis, anything that looks like an 'out' might be taken, sadly. Not smart to begin with, they're susceptible. It's sad.