Okay, I've been running on my dynasty and not checking on this again, so I might be a bit late to explain this.
Well if you need to fulfill a wish, then setting the ground by your home on fire and a paparazzi caught on fire, then I guess its ok. However purposely going to the community park and setting ground on fire seems wrong.
Perhaps I should explain first: why a community park? and not home lot?
Because when I set fire on home lot, household member would immediately got their queued activity hijacked and they have to running o the fire and doing the silly fire dance, and me as a partially obsessive compulsive watcher find this incredibly annoying.
So, if I do fire blast on a park, who cares if the random townies activity had to be interrupted? I certainly don't, they are not controlled by me.
But sometimes there are too much townies surrounding the fire and I have no idea what s wrong with the path-ing but my sim can't reach the fire because someone blocked her path and suddenly a sim caught on fire. And I think 'Aaaaw! not again!'.
I personally felt bad too if I don't help the sim who caught on fire, but the with the path problem, it could take hours before I could finally succeeded. So, I have to ask those questions above, about the okay or not to ignore the sim who caught on fire.
My sim is a witch and would occasionally has a wish to hit a fireblast. Hence the reason for occasional burning on the park. In reality (or real life) perhaps they all had developed phobia of fire already.