I don't claim to know much, but there is one thing I know to be true.
Responding to negative actions with hatred has one possible outcome: even more hatred. This very simple truth has been recognized in the world probably eversince it exists, and yet most of the time we are still unable to encrypt it into our hearts.
The purpose of terrorism is not killing people. Mass-killing is a tool, as well as generating a very high level of fear, but it is not the purpose. These terrible acts of violence crave our response. They stir up the entire population of the world, and live on through our general persisting reaction to them. They aim for our feedback, and the more mediatised these events are, the better they seem to hold everyone in a fear-based world. What better (and more radical) political tool then that is there? Not fair-play, but hey, it's politics after all.
All this is, of course, not to say, that we should stay passive and ignorant. How could we? It is our nature to react, and that is exactly what should be done. But instead of feeding a state of despair, which shortly closes us up in frustration and leads to becoming bitter, hateful, distrustful and incapable of real compassion and love, the only way we can contribute to a positive change is, by opening our heart and showing compassion through prayer and positive vibrations.
Shock and grieving are part of this process. These initial emotions point to you actually having a heart. It's a good thing, allow yourself to be shuddered. Acknowledge your fear, it's there. But walk past it. And open your heart in prayer or meditation (whichever silence resonates with you more, you do that). Please remember, always: love is the one reaction you can have, through which you can actually change anything in this world close to you, as well as far away. Open your loving heart! Compassion is not in your Belgian-flag profile picture on Facebook. Compassion is in your heart. Search for it within you!
Y'all might want to read this article here. Kai is a peace worker; he was running PATRIR for years, and is now the director of Department of Peace Operation. He has a clear vision and an open heart, revealing reality in a couple of paragraphs.