My answer was in my earlier post ... repeated below. The intent is deliberate, calculated and vicious and the punishment MUST be equal and send a serious message.
The arsonists know the difference between right and wrong. They understand that the fire may turn into an inferno and that's why they don't light them on wintery wet days. The objective is mayhem and maximum impact.
They light fires when the public is most vulnerable and most at risk , they light them knowing the potential for the fire to get out of control and in fact hoping and planning that it will. They do so believing they wont get caught. That doesn't make them "sick". It makes them "evil" 15 years imprisonment to life.