You've got to be a little sick in the head to take a moral stand. Even more so if you've done it without financial or personal reward, or expectation of acknowledgement or acclaim. That, it seems, is the tacit consensus at Bradley Manning's court martial. Last week, it heard expert witness regarding the medical and psychological factors which might mitigate or explain his decision to leak classified files to WikiLeaks in 2009.

It's tempting to see this testimony as verging on the pathologising of political dissent. In the Brezhnev-era Soviet Union, writers and activists were commonly detained on mental health pretexts. The logic was that the state was so obviously correct in its policies, only a lunatic could think otherwise. By treating its critics as symptomatic, the regime could deny its opponents the dignity of a criminal charge and the opportunity to contend rationally with their accusers. Torture, drugging and incarceration could be carried out under the guise of treatment, and done so indefinitely – in some cases, inducing chronic mental health problems, closing the causative loop.

But Manning's case is not comparable. Put alongside his own account, the diagnoses of fetal alcohol syndrome and gender dysphoria seem justified and accurate. Furthermore, the expert witnesses have noted that, in other areas, Manning's behaviour falls outside standard diagnostic criteria. In short, it's all a bit more complicated, and taken in the round, points in another direction – offering less of an insight into Bradley Manning's personality, and rather more into yours and mine.

Because the implicit corollary to all of the above is that a better-adjusted private first class in Bradley Manning's position would have watched the Collateral Murder video and done … nothing. Sure, he might have been mildly concerned or shocked, at least at first. But he'd have accepted the comforting constraints of rules and regulations. He'd probably have told himself that his superiors knew best, and resigned himself to the fact that such things just happen in wartime. Whatever the case, it was not his place to make a fuss, but rather to stick to the upkeep of the infrastructure that sustained and made it happen.

I think we can take this a little further still, and guess that another part of our hypothetical Manning-stand-in's well-ordered brain would have added that these matters were not his problem. Grotesque as they were, they posed no direct threat to him, his family or his friends. And his more realistic, grounded imagination might have accurately envisaged the life-wrecking catastrophe he'd bring on himself by exposing such material. He'd also be worldly enough to know that even if any of it came to light at a later date, he wasn't going to be held responsible for having not revealed it. He'd know there'd be safety in the huge number of other normal, eyes-averting types like himself.

That's what a mentally-healthy, self-confident, ontologically-secure person would (and should) have done, according to the court martial's brutally low opinion of the regular human being. In this, it is almost certainly correct. Because others – many others – must have seen the same material that Manning eventually leaked. Normal people, presumably: people like us.

Or maybe not like you. For whatever cocktail of reasons, maybe you'd have done as Manning did and with it, terminated or at least jeopardised any possibility of a normal life, freedom of movement and association, relationships with friends and family, and much sense of belonging to a country and a people. But until you're in that situation, you can't know; and let's face it, you probably wouldn't. You're not crazy.

I know that I didn't. As a young officer in British army, I had the chance, albeit on a rather smaller scale. Nothing on the scale of Collateral Murder – just the standard toxic background hum to which every frontline GWOT soldier is privy, which hangs around forward operating bases like the smoke from burn-pits. For instance, instead of shaking my head sadly, I could have demanded details when I heard rumours of wanton destruction and excessive force – generally attributed to other units, effectively untraceable but highly believable, and circumstantially confirmed by the walls of portaloos, on which the graffiti hovered between boast and confession.

Chris Yates (left) on his Challenger II tank in Iraq

Or I could have interposed when I heard a visiting tabloid hack whipping up troops' bloodlust, encouraging them in their inflated bodycounts. I could have voiced my concern that patrols were provoking firefights in order to generate material for YouTube uploads. I could have tried to chase up at least one example, made a nuisance of myself to senior officers – and if that didn't work, tried to find one of the few journalists who was not too preoccupied with their own embedded heroism, and told him or her.

Later, some of my friends and peers did just that. As they found, it achieved little apart from a swift(er) transfer to civvy street. But even then, there might have been some benefit, unseen, unadmitted. Either way, I'll never know, because I didn't try. I didn't try because I was a normal, mentally-healthy, mature, well-socialised individual – which is also to say that I was weak and selfish, more worried about my career than the suffering of others, more concerned with my own comfort and status than the values and standards I was supposed to be upholding.

All the while I vaguely hoped that one day, someone would say something. I just didn't want that person to be me. That bar was too high for my moral courage to clear. What I did instead was stick to what everyone around me was doing – putting up with the mortar bombardment, IEDs, being shot at and shooting back. It wasn't as dangerous as it sounds (ultimately, the battlegroup did not lose a single man in combat); nor was it out of concern for the rules, nor out of a sense of duty. It was simply the sane, slack, less risky option.

In every society, democratic or totalitarian, the sensible, grown-up thing to do is to commit to the long haul of sleazy conformity. The rewards are mostly guaranteed: if not freedom or happiness, then respectability and degree of security. What spoils it is the obstinate few who do otherwise – those, absurdly, who actually believe in the necessary fictions; enough to be moved and angered by the difference between what an organisation does in reality and what it says in public.

In this respect, the whistleblower is arguably more mindful of an organisation's stated values and standards than the vast majority of its members and affiliates – so much so that keeping quiet or going along with it or walking away is not an option. The final irony lies in the whistleblower's faith in normal people, the assumption that they will welcome being less deceived, and use the revelations to press for reform in their governments and institutions.

For these delusions, whistleblowers have been punished, again and again, throughout history. But for whatever reasons, still they do it. In a ghastly way, those Soviet pseudo-scientists might have been right: viewed from the perspective of a normal person, such an individual would have to be a little sick in the head.

• Editor's note: the photo caption of the author on his tank misidentified the location; no Challenger IIs were ever sent to Afghanistan. The caption was amended at 9.15am ET on 20 August