We're all out there with different goals, and for different reasons. I personally tend to prioritize all day comfort for high mileage hiking over night time comfort. Consequently, I'm happy to rely on a poncho for shelter, a postage stamp foam pad, and no changes of clothing or other luxuries. For those who value the comforts of camp, this might be a stupid approach, but it appeals to my minimalist sensibilities.
For me, stupid light would be bringing a pot too small to boil the water I needed for a meal/drink in one go, as this would drop my efficiency.
On one fast paced trip, I brought no insulation other than my 35 degree sleeping bag, using that to wrap myself in at stops. It dropped down to 28F or so one night which was pretty chilly (but not unbearable). That was probably stupid light. Then again, I achieved a personal best in mileage/pace and had an awesome time, in part because the additional challenges. Next time though, I'll add in a 3.5 oz vest, with no perceptible change in pack weight.
Stupid? Not so sure
From the same trip