It would only be stealing if he was deprived of something.
I think the RIAA & MPAA might disagree with that statement.
Well, this is what a libertarian utopia looks like, kids.
I think you're confusing libertarians with anarchists. Sure, they are at the same end of the political spectrum but libertarians believe in limited government not no government. Most libertarians would agree that one of the few areas that government should be involved in is protection. That includes such programs as police, fire & military.
As for "why not put out the fire and then bill him", the $75 fee is not to put out the fire, it's to keep the fire department running when there *isn't* a fire. You can no more pay the bill after you need the service than you can wait until after you get cancer to start paying for medical insurance. The system can't work that way.
That's a flawed argument. As many others have suggested, you would not bill him the insurance premium ($75) but rather the cost of service (whatever that may be) which would include the cost or having the firefighters be on-call.
While I agree that you can't expect to get medical insurance after you get cancer, you can still get medical treatment if you are willing to pay for it yourself.