the hulk may do a good job of fighting crime
Because people learn best through trauma. Your immune system is a good example of this. Getting the flu sucks, but if you never got sick, then your immune system could never get stronger.
That monster proved the destruction, then people can seek the constructive way. Godzilla is a series of good films on this topic.
Spice things up
I don't think it does, but, looking at present government leaders right now, it seems we've got quite a few. Not going to mention names. Figure it out for yourself.
In every religion, there is a prophecy that god will return and eliminate evil and slay evil doers.. be it return of christ, mahdi messiah in islam, or kalki in hinduism etc. god makes a come back in the form of monster who slays other small monsters, so that a big monster like him (god) continues to rule.. posing as benevolent father