I don't want to lose 1/4 of the picture just so it'll fit neatly on my screen without black bars. The worst is when the first HD release of a program mastered on film is in 16:9, so we never get the full picture in HD and have to choose between higher resolution and seeing the whole damn picture
Seinfeld suffered from this when it was put on Hulu in 'HD'. Nauseating!
It trains people to not really care about proper aspect ratios too. I'm rewatching Twin Peaks with my roommate since she's never seen it and I was like "oh, I have the blu-ray version of all 3 seasons and the log lady intros/missing pieces/etc on my external HDD let's just watch it off of that". Throw it on the TV and of course it's in its original 4:3 aspect ratio. Immediately I hear "can you get rid of the black bars??" and I have to pause the episode to inform her that I'm not losing 25% of the picture just to satisfy her insane desires for 'FULL SCREEN'.
Always wind up just putting on this video to explain to people why I'm not going to 16:9 from a 4:3 video!!!
I watched Twin Peaks a while back, and I was so happy that the HD releases are in 4:3. When given the choice between HD and original aspect ratio, I nearly always choose original aspect ratio.