Why didn't the Alliance destroy The Reavers?

Question

In Serenity, we learn that

The Alliance accidentally created the Reavers.

So my question is, why didn't the Alliance destroy them? There were fewer than 30,000 Reavers and the Alliance had a much larger military.

We also learn that

The Alliance knew that the truth about the Reavers could (and did) severely weaken them.

So why did they leave them alone for so long? It could be argued that waging war would bring too much notice but surely just allowing them to sit there and send out raiding parties would make them more known to the general public.

Answer 1

I'm not sure that this is ever addressed in canon, but logically;

The Reavers may have proved useful to the Alliance.

It is well known that not all of the planets in Firefly and Serenity were happy to become part of the Alliance, with an army of "Browncoats" fighting for independence from the Alliance (and ultimately losing). The Alliance is made up of a series of "core planets", with planets further out classed as "outer planets" resembling the 19th-century American West and being generally less civilised than the core planets.

It was the outer planets that made up the bulk of the Browncoats, many of whom still detest the Alliance after the war was over (see: Malcolm Reynolds). Politically, these outer planets are officially under Alliance control - but they often have very little regard for the Alliance and their attempts to control them. Naturally, the Alliance would be aware that they are not popular in these areas, and have probably considered the possibility of another Browncoat uprising.

So from the Alliance's perspective, the Reavers prove to be a useful resource. It is the outer planets (those associated with the Browncoats) that are most often attacked by the Reavers, planets that are unable to defend themselves and as such rely on the Alliance for protection. This reliance means that the outer planets may believe it too dangerous to attempt to "secede" from the Alliance in another civil war, guaranteeing the Alliances continued control.

In conclusion, the Reavers pose nearly no threat to the Alliance, but help ensure the continued loyalty of the outer planets.

Edit: It has been bought up in the comments that the Alliance might deny the existence of the Reavers. Even if they do, I'm sure the outer planets (which are aware of the existence of Reavers) feel more secure under Alliance control, so the end result is the same.

Answer 2

The Alliance's hold on the Outer Rim planets is much less secure than the inner worlds; this is the whole reason people like Malcom and his crew continue to exist. Once the Alliance managed to push the Reavers so they were confined to the Outer Rim, it wasn't worth their trouble to keep wasting resources on them.

Consider the issue from the Alliance government's perspective:

• As far as they knew, everyone that knew the truth of the Reavers' origins was either dead, or a government official
• The population of the Core Worlds mostly considered Reavers to be a myth.
• The population of the Outer Rim assumed that Reavers were what happened if you tried to fly out past the edge of the system.
• The presence of the Reaver horde floating outside Miranda was keeping nosy explorers away from the planet

In other words, keeping the Reavers out in deep space served as a deterrent to keep the population from wandering too far away from Alliance control, and kept (unwilling) guard on the Alliance's dirty secret. On the other hand, starting a war with them would cost resources and people, and would likely get people digging into their origins.

There was no upside for the Alliance to fight the Reavers.

Answer 3

• They are very far from the Core, hence going there are destroying could prove more complicated
• Going there could unveil the role of the Alliance, and since most people never try to find out, it would have been a bigger risk than doing nothing
• It serves the Alliance, as a good enemy helps justify military measures