To quote an answer of mine from this very month, whose asker's account inexplicably does not seem to exist anymore. You may find it especially enlightening with regards to the "many stories" to which you refer:

I assume by describing Crassus' use of his firemen as "unethical" you're referring to the oft-repeated claim that Crassus would not put out fires until their owners sold him the property. The story's from Plutarch--and as far as I'm aware Plutarch alone--and the text says nothing of the sort. What Plutarch says is this:

ἐξηγόραζε τὰ καιόμενα καὶ γειτνιῶντα τοῖς καιομένοις, διὰ φόβον καὶ ἀδηλότητα τῶν δεσποτῶν ἀπ᾽ ὀλίγης τιμῆς προϊεμένων

He would buy burning properties and those next to burning properties, with the owners getting rid of them at low price due to their fear and uncertainty.

What Plutarch actually describes is not Crassus' refusing to put out fires until he could buy the properties, it's Crassus arranging to buy up endangered property while putting out the fire. Nowhere does Plutarch say that Crassus would refuse to put out the fires until after he was paid, and in fact he doesn't even say whether the sale would occur before or after the fire was extinguished, although his comment on the fear of neighboring landlords suggests that this is happening while the fire is still being fought.

The fear of the adjacent landlords was a real one. Apart from the near-inevitability of nearby properties to catch fire, given the poor quality of Roman insulae and the total lack of building codes for the entirety of the Republic and much of the Principate (during which time such codes were never enforced in the city), perhaps the most effective means of preventing the spread of a fire through the city was the demolition of nearby buildings, creating a dead zone into which the fire could not move. Indeed, this was so common that metaphors for demolition to prevent fire crept into the Latin idiom, perhaps most famously in Catiline's great quip as reported by Sallust: "Quoniam quidem circumventus", inquit, "ab inimicis praeceps agor, incendium meum ruina restinguam," "'Since indeed I, surrounded, am driven headlong by my enemies,' he said, 'I will extinguish my fire by demolition.'" Plutarch gives no explicit reasoning for Crassus' actions, and colors this part of his narrative with the suggestion that Crassus never did anything for anybody without expecting some benefit, but on the other hand we can quite easily imagine what Crassus' argument might have been. The jurists of the Principate and later discussed under what grounds one could demolish a neighbor's property when under threat of fire without risk of lawsuit, and in the Republic this was a legal point surely totally up in the air. We have no attestation of Crassus' public argument, if one was given, but it is hardly difficult to see how buying all adjacent lots to a fire would vastly streamline the firefighting process, given the private nature of all fire companies other than the highly inadequate staff of the tresviri nocturni during the Republic.

Besides demolition, the "nuclear option," so to speak (if one frequently resorted to), ancient firefighting methods were primitive. Pliny and the Digest mention some kind of fire pump later in the Principate, but its nature is unclear and it seems to have been a curiosity more than anything else. Like all fire companies until really only a few decades ago, the fire companies of the Roman world used bucket-brigades and rags soaked in water or vinegar. Like all pre-modern fire companies these methods were not especially effective--hence the frequent reliance on demolition, which at least kept the fire from spreading. Containing fire, rather than saving the property on fire, was the real threat. Insulae in the city were usually cheaply made, with thin wooden walls or walls of rubble faced with cracked stucco or brick. They shared walls with each other (still a common feature in modern Italy) and were many stories high with single cell-like rooms and no accommodations for escape from fire whatsoever. The streets of the city were extremely narrow, sometimes only a couple abreast, with projecting rooftops that hung over not only the street but even buildings on the other side--any traveler to the alleyways that crisscross modern Rome outside of the tourist-traversed main boulevards will find more or less the same thing today. Not unlike far too many forest fires and wildfires even today the main goal was to save the surrounding area, not the individual doomed structure