Thanks Sudhanshu for summarizing Dershowitz’s arguments. As he’s someone who’s felt perfectly comfortable making a living defending utterly repellent people with spurious legal arguments, one must first note that anything he says or writes must be treated with the same skepticism we’d reserve for statements made by people like Goebbels, Stalin, and Mao (or, updated somewhat, Putin, Trump, and Johnson). More importantly, however, his armchair middle-class ideas have zero relevance in the real world. Torture is the least effective form of interrogation known, because someone in fear of pain or death will say anything at all in order to make the torture stop. Thus the argument against torture is not grounded in abstract moral issues but in the very practical issue of efficacy.
I have several friends who are former special forces operators, all of whom passed through training that equipped them, for a short time, to resist torture and thereafter to provide information that is worthless to captors. None of them hold the belief that any useful information can be extracted by means of torture, and they’ve seen real-life examples in addition to their training.
Most famously, the CIA tortured Khalid Sheikh Mohammed by waterboarding him 183 times; the agency later acknowledged that none of the information he provided under torture was useful. It merely sent them on wild goose-chases.
Perhaps the best response to Dershowitz’s attempts to ensure that US citizens always acquiesce in government-sponsored torture is to take him to an unknown secure location and apply certain techniques to him for a while. No doubt this would serve to enlighten him and perhaps make him fractionally less likely to write silly little books thereafter.