The point is, torturing can only make it worse. That's pretty indisputable, isn't it?
I don't think it matters in most cases. Once stories are being told for propaganda / recruiting purposes, it's a negligible bonus if they turn out to be true. Veracity has a statistically insignificant effect.
I may be a wee bit cynical.
This is a minor quibble, though, and I agree with your point in the main. Torturing can theoretically make things worse from a PR perspective. I wouldn't say "only", and I don't think it's indisputable, because I think the effect is usually going to be zero. I can't think of any way it could make things better, though.