Salmon in general don't eat when entering natal rivers to spawn. Fishing to spawners was not the topic of the article Overmywaders2 posted, quoting some well known fishermen, but fishing to resting trout in 'sanctuary' water. It further argued for TFFO regs limiting angling to surface fishing, or intermediate fishing using a line with maximum sink rate of 1"/ps, and no weight on leaders or flies. It essentially establishes the upper quarter of the water column as the water that may be fished and no deeper, even while acknowledging trout do the majority of their feeding below that column.

I argue that resting trout are no more likely to take a fly than a natural regardless of the water depth they reside in, and fishing to trout in/near the surface is no more sporting than fishing deeper.

Whirlpool,
Which doesn't explain why trout mouth/eat non-food items unless they are finding nutritive - or digestive - value in some of them. Further, I've read nothing to indicate they do so outside of feeding activity; that is, they certainly aren't expelling food items while entertaining themselves mouthing things that have no food value. They do this in the search of sustenance, i.e. feeding. Spawning/territorial strikes may be directed towards streamers, but we can't extrapolate that to nymphs, wet flies.

At length, I've watched large trout resting in water anywhere from knee-neck deep, or hanging under the surface, not feeding. This is why I disagree with arbitrary definitions of 'sanctuary water' and cordoning off the lower 3/4s of the water column. There is no sanctuary water that is also not used by fish to feed. Their sanctuary (outside of not fishing over redds) is not eating and letting our offerings pass by.

Aurelio,
Yes, we've all had days like that!
I'm not arguing fishing dries is less sporting or easier (though it often is). It was to challenge the notion that subsurface fishing - anywhere in the water column - is less sporting. Neither is ethically superior; we fish for our pleasure first, and welfare of the fish second.