Do terrorists have no conscience?

Do terrorists have no conscience? And if they do then how can they live with themselves after killing people...people who they never even knew?
And if they do then are so brainwashed that they believe they are doing right? Are they actually mad?
If so should they be pitied?
I mean you are only wrong if you know that you doing wrong and you continue to do so...
So should the people who train be blamed? Do they do this for private gains? Who is to blame and how can religion be responsible? I mean anyone who believes in God sincerely would realise that religion is something sacred and private and universal. Religions are just different ways of communicating with God. But even the heart is enough for that. To listen your conscience is the truest religion.God cannot like his own creations being harmed...least of all by themselves.
Why don't people understand this simple truth. It's so sad and yet mind boggling.