The Death Star was a civilian project. It was actually a combined project civilian and military, in which the civilian project (a super-laser that can destroy planets) was encompassed by a large military installation (a massive, mobile space station). The latter helps to insure the former doesn’t fall into the wrong hands.
Hear me out.
Granted, the Galactic Empire is headed by some big nasties. But that doesn’t make the Empire itself big and nasty, even when they paint everything grey, keep the lights low and blue, and bid each other Dark Greetings(quote here). Big nasties seem to have a propensity to get into power even in the most well-intended of civilizations.
The Tarkin Doctrine is a philosophy in statecraft that is in terrestrial use today, only we call it Gewaltmonopol des States or the Monopoly on Violence. The notion is that only the state retains power to force anyone to do anything (and can muster overwhelming means to do so), and anyone else who wants to force someone to do something (say to pay for the garden he destroyed driving over it) appeals to the state for redress.*
At the personal level it serves as a point of confirmation for armed angry drunken people before they gun down those that annoy them. (Warning: You are about to commit murder. Proceed? y/N).
Given the human tendency towards obeying the law, reciprocity and avoiding harming others (even preventing harm to others). Major transgressions such as homicide are uncommon per capita, but is still seen in the fringes of civilization such as the lawless West, or more modernly in places where law is poorly enforced (e.g. impoverished and minority communities.)
A more statistically evident difference can be seen where there are high-value markets heavily competed over by large companies. Left to their own devices, they will openly war on each other, id est hire armies to attack the facilities and resources of their rivals. The reason multi-national companies don’t do this (openly) is because the state maintains laws against doing so and can muster a vastly bigger army by which to enforce those laws.
That said, even at the larger scale of feuds between multi-national corporations that involve military engagement, the Death Star super-laser would cause way too much collateral damage. As is demonstrated by the game Chess, the actual belligerents in any dispute really come down to a small group of officials, or even singular individuals. The clash of armies emerges when those individuals have the means to interpose forces between themselves and their enemies. Thus, in an interdiction by a state, the objective would be to narrowly target the commanders to be brought to justice. When they are detained the fight becomes moot to their subservient forces.
Using the Death Star to destroy a populated world to strike at its king is overkill.
In World War II, the atomic bombing of Nagasaki was compared to the firebombing of Tokyo which averaged (I’m guessing with rough estimates) about 200 B-29 payloads a day of incendiary bombs over several months. The threat of the atomic bomb wasn’t that similar destruction couldn’t be done conventionally, or that the nuclear bomb was more horrible than conventional warfare, but that the destruction was done by one action. The Death Star super-laser can be considered similarly. It serves well not as a standard weapon for Imperial intervention considering the amount of collateral damage that would occur. But the notion that the Emperor could, with a signature, authorize a single shot and make your entire planet go away is a substantial threat that might give pause to even a lord of many worlds. This was Tarkin’s point (the fact he chose to use the weapon on a non-military, Imperial settlement notwithstanding. That was career-endingly stupid.) But having the Death Star in your system is not unlike the US parking a carrier in the Persian Gulf while negotiating with Iran.
So what is the Death Star‘s civilian purpose? Mining.
Planets are full of minerals that we continue to use. And we use a lot of them. But with even Imperial technology, digging deep to get to outer core minerals takes formidable construction to keep the mines from collapsing in on each other. The deeper the mine, the stronger the superstructure necessary to keep it open. (The problems of superdeep mining a planet intersect greatly with the problems of running a transit tunnel through a planet’s core**
This is where a super-laser comes in. A tiny fraction of the power that exploded Alderaan (around twenty-million times less) could nicely crack an unoccupied-but-mineral-rich planet into manageable chunks to be individually harvested.
Mining messes planets up for purposes of settlement and colonization, and the more the Empire extracts from otherwise uninhabitable planets the less they have to scar the surface of habitable ones. The Death Star super-laser presents a means to speed the harvesting of uninhabitable worlds with the added advantage that core minerals are accessible quickly rather than only after the surface has been stripped away.
The question still remains, when the power consumed by a super-laser mining blast is of the magnitude of the total output of a sun, how many planets would have to be harvested before the Death Star pays for itself?
In the meantime, jobs!
* Of course, this is a hypothetical model. This presumes a Tuckfun of systems work the way they’re supposed to, and as we’re discovering in the Internet era, we are far more removed from this ideal than was commonly believed, not only that justice systems do not work very often, but fail in ways society didn’t expect.
** Some of these concerns also intersect with the dynamics that would occur with an ocean that runs deep into the outer core. How such a system can stabilize without collapsing is a popular topic among young Republic planetologists.