Some people need religion to stay sane. They follow religion, obeying the rules and morals, which a religion sets out.
Honestly it actually gives morals to people but humans being humans, have to fight over different views of religion. Like America starting war for oil :carling:
Without religion they would have no hope of life and see life as a pointless, waste of time. When people say their religion is wrong, they automatically get defensive about as it's so important to them.
Without religion there would obviously be less religious causing war but there will always be war between humans (humans are greedy, lets face it). War will still be at large on earth.