I think that sometimes there's another factor that gets overseen when discussing torture.
The "problem" that I believe is also tried to be addressed with torture is the view that the society that "supports torture" (via their government, even if against the opinion of most people) can't let leniency get in the way of righteous retribution against their enemies.
Imagine if someone invents a pill that is literally the "truth serum", and that the subject taking it can't lie for say an hour or so.
Would that end torture? If torture's only objective is to get information then it should.
But what if torture is really filling another role? one that is not satisfiable by information but by inflicting pain on your enemy?
I'm not defending torture by any means, and I do think it should be something that we as humanity should strive to end. But it seems like more often than not you can find people that would not defend torture, "except in cases of extreme need", i.e. when they need retribution.
It would be interesting to do some research on what victims of crime and violence, and their families, think about what it would be "fair" to do to their offenders. Maybe it turns out most won't be willing to inflict pain in others, or maybe it turns out most people are vengeful and would like to see their enemies suffer.
If the case is the latter, then I think the main problem with torture would be not as a tool to obtain information, but as a tool to inflict retribution.
What if a society that is mainly governed by people of the second kind get a hold of the ability to torture? e.g. CIA interrogators, people that sign torture orders, etc? then in their minds it would be justifiable, even if the activity doesn't yield any useful information.
If it does, then they get the information AND retribution. If they don't get truthful information then they still get retribution.
That's why I think torture is a subject so hard for officials to understand the damage it can cause. As long as they think retribution in this form is OK, then it will be very hard to end this practice.