Sean, I expected better from you! :-)

You hit a bump or are riding on rough road you want some deflection and dampening. Generally, more flexy bars will be more comfortable and the material play a major role in dampening. Keep in mind that I don't think any bar is going to flex that much from the stem to the hoods.
So... It easy to make a stiff, cheap handlebar. You can use thick wall metal can bend it the simplest way possible, then heat treat it the fastest way possible. One reason people may think AL bars suck is because the stock units that come on most bikes are almost universally cheap, stiff units. It's not the material it's how you use it. Unlike frames, bars are open ended. Round tube AL frames shake the crap out of you because they can't flex well. Here it's open ended with free movement and we can fiddle with the material with less restrictions.
Here you can see, as implemented, an AL bar will flex just as much as a carbon one. Road Handlebar Review - Fairwheel Bikes Blog
As for dampening, you've got the bars wrapped in tape and your body is enough of a dampener to kill the oscillations - plus you've got a big tire and dirt under you. In any case, you can make a comfy, light AL handle bar. Carbon allows you to shape the bar more easily, so you can make the part where your palm sits fatter and for the bar to have more bends. It'll be lighter, but like stems, carbon handlebars don't tend to be all that much lighter than the AL versions (30-40gr).

I have carbon bars on both my bikes, but I wouldn't buy a handlebar because it is carbon. Internal cable routing, flat top/aero profiles, and more contours make the difference for me.