OK, but when you're considering whether and how to fight a fire in a burning building there's no court to make the decision for you; and even afterwards, all the expert witnesses are going to be firefighters talking about the particular risks presented by the particular structure.

If the insurance policy draws a distinction between whether or not lives at risk when a non-subscriber's call is answered, then the insurance company may have a case as you describe. But your comment seems to assume this is the norm, whereas the questionnaires I've looked at don't make that distinction.

Remember such insurance policies (issued to a FD) are upon life and limb, rather than on department revenue stability. An insurance company would challenge a payout if they felt the fire department (perhaps because of bad training or staffing policy) foolishly ordered a crew into an impossibly dangerous situation resulting in injury or death, even if the property owner was a paying subscriber. In reality, fire crews sometimes have to let a property burn and just try to stop the fire spreading, because the presence of chemicals or an unsafe building structure makes it too risky to enter.