Let me be clear.
Driving a car is also a sakana to ‘everyone’ (by everyone you mean ‘many people’). In the event of a brake failure, or a loss of attention, or mistimed maneuver- many people could wind up hurt as a result of your decision to drive the car.
Blocking a fire escape presents a similar sakana. To block a fire escape for no reason would be senseless. To put a succa there is not senseless- if you want to have a succa and you live in an apartment, it is easy to see the sense in putting it there (since all other space accessible to you is indoors).
I am not saying that this means it is OK to do- au contraire. As it is a violation of code, it is just as wrong as double-parking your car or parking in front of a fire hydrant. Just that the folks crawling out of the woodworks to cry ‘sakana’ as of the same ilk as the ones who want to stop kapparos because ‘tzar baalei chayim’.