The fact that you and other insist on this really gets at the crux of this whole problem. There are two notable positions on criminality and punishment: yours, which is broadly that the justice system exists, at least in part, to deliver righteous punishment on the deserving, and the position of those appalled by the treatment here, which is that the purpose of the justice system is primarily to protect people, and then to deliver predictable, proportionate punishment of those found guilty to disincentivize criminal behavior. If you think that torture of someone detained but not found guilty might be justifiable if they're accused of a sufficiently heinous crime then you have an illiberal position that can and will be used to enable abuse of the criminal justice system to inflict extralegal punishment on anyone for any reason.

So rationalizations of why it’s appropriate because the person was suspected of XYZ isn’t going to land with them and is largely irrelevant.

But I don’t mind playing devils advocate.

Should the justice system force confessions out of murderers? No, because they are only potential murderers and we have historically been able to get innocent parties to confess. People with vulnerability such as mental health problems are even more likely to give false confessions. The goal of requesting testimony should be honesty not compliance.

This logic applies as well the drug dealer, drug users, and jay walkers. It’s a moral principle disconnected from any specific geography so even if we are not Japanese and have no intention to interact with Japan, we can say they have not lived up to that principle.

Makes me think of TNG (Season 1, Episode 8). Death for walking on the grass.

What is Justice anyway?