Since I feel that someone who murders or rapes someone should be spared little mercy, then by extension I feel this is an acceptable tool so long as it doesn't harm the innocent.
Are you meaning there should be no presumption of innocence, or are you meaning the lying should only be allowed after they've been convicted?
Of people who got exonerated through DNA testing during 1989-2020, 29% involved a false confession (https://innocenceproject.org/dna-exonerations-in-the-united-...).
> as it doesn't harm the innocent
The whole point here is that the person at this stage is presumed innocent.
>someone who murders or rapes someone should be spared no mercy
But we're supposed to presume "innocent until proven guilty". A suspect is only accused, not convicted.
That assumes the person in the interrogation room is the correct person to begin with. We have a fair amount of false conviction rates.
"Hell no" seems like the obvious answer, but you seem to disagree?