Defense Minister Song Young-moo on Wednesday appointed Col. Jeon Ik-soo, the judge advocate general, to lead an independent investigation into alleged wrongdoing by the Defense Security Command.

The appointment was made upon President Moon Jae-in’s order to launch a special independent investigation into allegations the unit drew up a document in March last year to explore the possibility of imposing martial law if public protests spiraled out of control after a court ruling on the impeachment of President Park Geun-hye.

The document contains an emergency military response to chaos in case protesters were to occupy important facilities after the ruling.

However, such an extreme situation did not happen, and there was no reason to review the document.

The document reportedly had a concrete plan for seizing regions with tanks and armored vehicles and crackdowns on civilians with paratroopers.

As shocking as its content is that it was prepared by the military security and counterespionage unit, which has no authority to mobilize troops. Such authority belongs to the Joint Chiefs of Staff. Why the DSC created the document should be thoroughly investigated.

Investigators must reveal the truth about many other aspects as well: Who initiated the plan, who ordered the DSC to prepare the document, to whom was it reported, whether the military had the intention to execute the plan and whether it really took action.

The allegations that the DSC spied on families of the victims who died in the Sewol ferry sinking must be clarified, too.

The martial law plan was allegedly predicated upon the worst possible scenario, but it could hardly have been executed in a mature democracy. And yet the act itself of assuming such a situation and drawing up a response plan should not be dealt with lightly. A similar incident must never happen again.

Undoubtedly those responsible should be punished according to the law. Military interference in politics undermines free democracy and turns back the clock of history.

But it is questionable if this issue is so urgent and grave that Moon had to order an investigation independent of Song’s command during his state visit to India for a summit.

The document was brought to light in March but remained off most people’s radar, then it drew attention again with Moon’s order Tuesday.

It seems hard to view the document as serious evidence of an attempt at a coup. Imposing martial law would have been practically impossible at that time and so would be now, too. Probably that is why the document did not capture people’s attention in the first place. Song reportedly tried to deal with the issue as part of his plan to reform the entire military, DSC included.

Then Cheong Wa Dae ordered an independent investigation suddenly, mentioning the gravity, seriousness and explosiveness of the issue as if the DSC had attempted a rebellion.

The main opposition party attacked Cheong Wa Dae, saying it targeted a hypothetical situation in order to boost its anti-corruption drive and strengthen support for Moon. Some conservative politicians argue the military did what it should. As the last bastion to defend the country, they say, the military must consider the worst possible situation and draw up plans for it.

The document can look unacceptable or understandable, depending on an individual’s viewpoint. However, one thing is clear: Such a plan must never be created again.

It is worrisome that even before the launch of the investigation, some people demanded the dissolution of the DSC or uttered the term “conspiracy for rebellion.” They are going too far.

Like any other organization, the unit has problems, but be that as it may, it is unreasonable to say it was plotting a coup.

The military security unit was once condemned for interfering in politics and spying on civilians to help rulers retain power. Those acts must be rooted out this time, but its proper functions should not be slighted at all.

The investigation may as well be oriented toward ensuring the unit can devote itself to its proper roles, not toward wiping out its functions. The government must not throw the baby out with the bath water.