I disagree.
What if you have the power to stop it, but at great personal risk to yourself? We're talking about stopping a raging housefire, not helping some poor old woman cross the street.
Alternatively, once you work to fix something, you're generally going to be held responsible if you screw up. So, what if you have the power to stop it, but as a result of your actions you actually make matters worse and the homeowner sues you? Hopefully you have insurance, but who pays for that? Well, in this case, not the homeowner.
What if by stopping the fire on this person's house you miss a change in the winds and his neighbor's crops (and thus his livelihood) are entirely destroyed by the fire that licked his land? What makes one person's property more important than his neighbor's?
What you mean to say is that many people feel a moral imperative to help others. This is true. However, we all must weigh our moral imperatives against the potential harms to ourselves and others. Unless everyone on this board is Mother Teresa, you're not doing everything in your power to help your fellow man. Similarly, there is the concept in law that there is no duty to save. You see a child drowning, you jump in to help, you hurt the child more while trying to save it, and you are responsible. From the point you decide to lift your hand to assist you are putting your faith entirely in the good will of the parents...hoping they won't come back and try to harm you for your "good" deed.
Firefighters are brave and we hold them upon a pedestal in our society. But in the end, firefighters provide a service, and should be paid for it. Firefighters risk their lives and then go home to their families who need a roof over their own heads and food on their table. To not pay for firefighter protection is denying them property the same way a fire might deny you of your own.