Hilzoy cautions us against thinking that sleep deprivation is a kindler, gentler form of torture:
The various kinds of psychological torture, of which sleep deprivation is one, are just as disturbing as physical torture; possibly more so, since their aim is to induce regression and learned helplessness, which is a way of inflicting serious psychological damage. Keeping someone awake for long periods of time, or using sensory deprivation, isn’t awful in the obvious ways that, say, beating someone to a pulp is. But even though it does not leave visible scars, it’s profoundly wrong.
Another point I would make is that you’re obviously not going to use extended sleep deprivation in a “ticking bomb” scenario to prevent an imminent attack. Doing enough sleep deprivation to break down someone’s personality is a days-long process.