They wouldn't be if people stopped taking them but we're seeing the reverse trend, there's more demand for air travel than ever.

Without taking the fact that they don't have the equivalent of catalytic converters into consideration, planes are shit for the environment. Their impact is disproportionate compared to their actual emissions because it's done at altitude and from a fuel consumption per passenger distance perspective they're not good either and they're worse the shorter the distance they travel because they burn a shit ton of fuel for the takeoff. You can take a Chevy Suburban with three of your friends and travel the same distance and you'll pollute less. Only you and your friend? In a Honda Civic you're burning less gas per passenger than if you travel in a plane that's full of passengers!