We should never fear madness, only intelligent madness.
When a man loses his wife and children he may grieve or accept it and seek to move on. Few seek revenge; but when they do it is coldly directed. In the Islamic world it may lead to a blood feud, but directed at the West that hatred will grow.
Hatred combined with knowledge, has led to the downfall of Empires but his unique life has given him the ability to go much further. He understands the modern world, and, as a result, knows our Achilles heel, and has the drive and desire to exploit it - yet he lacks just one thing - opportunity - until now.