Perspectives

I think at least part of the importance of literature, or movies, or a story in basically any format, is the ability to show a different perspective. Besides the few laughs or tears you might get from a comedy or tragedy, the greatest impact of a good story is to show you things from someone else's perspective. This isn't exactly Aristotle's ideas of a "catharsis" after a tragedy, but I think it's related-- you feel "fear and pity" watching a tragedy because you are at some level understanding the perspective of someone who inevitably ends up in a terrible situation. 

Comedies can show you a different perspective as well as a tragedy can. Maybe a comedy might tend to show a different perspective from a tragedy, but that's what makes having both more important. And if you think that tragedies are somehow more meaningful than comedies, then to me it just sounds cynical, and maybe you should go read/watch some comedies for a change. 

I couldn't really come up with a particular comedy to defend. Also, and this is a bit of an afterthought, but when people write tragedies they're probably at least attempting to put in some kind of greater meaning (regardless of whether they succeed) while there are at least some comedies that are made just for entertainment, which might contribute to comedies being seemingly meaningless, when really it just means you have to look harder for a better comedic story. But that's just a theory.