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The best response I've read to this, by a former interrogator, was that waterboarding is actual drowning, simulated death.
They used to perform this technique in training at SERE High-Risk C, a course designed to teach certain military assets at high risk of capture how to resist and endure torture (not how to conduct torture).
When I went through the course, they had suspended it under a safety review, so I didn't have the pleasure.