Not sure where you're drawing the line of stupid, but all the light bars of recent years are 31.8mm - and a 22% increase in diameter is nothing to sneeze at. And we'll say nothing of the stem's clamp holding on tight enough to prevent rotation...

A drop bar could probably be 80g or more lighter at 31.8mm than 26mm, without compromising any strength. Thinner walls may be more subject to forming stress cracks from scratches, but if the bar is flexing much less it's pretty academic.

I'd draw the line at 220g for an ally road bar, myself... not sure about carbon ones.

Given carbon needs the protection of clearcoat against UV and moisture, and bars cop stem clamps, brake clamps and cable rub, I'm not sure it's a very clever proposition in the long term.