Lettuce is a vehicle to transport refrigerated water from farm to table. When we switch to vegetables that are twice as nutritious — like those collards or tomatoes or green beans — not only do we free up half the acres now growing lettuce, we cut back on the fossil fuels and other resources needed for transport and storage.
I do love salad because I love the delightful crunch and refreshing feeling it leaves in my mouth.
I guess whether it does have as much nutrition and is worth the cost is subjective. But I guess, as with design, even food needs has an aesthetic element. The visceral sensation that fresh juicy vegetables give to the person eating is far more powerful and lingering impression than numbers about their nutritional value.