Why do some religions hate each other?

Because some religions are told to kill everyone who does not conform to their faith... the people who ignore this tidbit of info are thus deemed "moderates" while the ones who faithfully follow their teachings are deemed "extremists". Other religions involve teachings of loving your neighbour as yourself, and turning the other cheek. People who follow this are not generally noticed by the mainstream, while people who do not follow this are quickly pointed out for their often-verbal association with a certain faith.