starone - "Wonder why we like being frightened!"
This theory is entirely mine - but I think it is based on logic -
although 'civilised', our veneer of civilisation as actually very thin, and a large number of the aspects of primeval man are still with us, but no longer used.
One of these is the 'fight or flight' mechanism that floods our systems with adrenaline and shuts of none-essential veins and arteries to prevent blood loss, dulls our pain sensors and so on, all designed to allow primeval man to fight of survival.
Now we are far more sophisticated, but this sense remains dormant, and I believe that the mind enjoys stimulating it under 'safe' conditions.
We know that films will not hurt us, that we will not come to harm on rollercoasters, but the adrenaline rush is still valid for our minds and experience, and we actively seek out stimulation for it.
Like I say, it is my own theory - believe it or not as you wish.