Why a lithium battery is a dangerous battery than alkaline battery?

I hear that lithium battery are not easily as rugged as alkaline or carbon zinc, not becouse of the poisonous nature of these battery but they say its unstable, not easily change and always explode/ is this really true? but how come there are so many lithium battery in the market tody (laptop battery, cellphone, PDa, even my Ipods use lithium)?