The filming of Schindler's list, as you might be able to imagine, was very sad. (In case you are not familiar with the movie, it's about how Nazi soldier Oskar Schindler saved the lives of over 1000 jewish people.) Day after day, they had to witness the same depressing tragedies that, sadly, actually happened. It got to the point that the movie's director, Steven Spielberg, had to call on comedian Robin Williams to send out comedy tapes in order to keep the cast and crew out of depression. I would have to say that that was necessary.
Who doesn't like a good laugh? Growing up I laughed myself to tears when I first saw Dumb and Dumber. But I don't consider that movie is a comedy that makes everybody laugh. Comedy serves for the purpose of triggering people's sense of humor. People have different kind of humors. For instance, I like to laugh at myself when I speed my bike and make sharp turns, and ending up having an intimate moment between my cheek and concrete. I did not need comedy, but simply a stupid fall. Because I do not need comedy to engender my humor, therefore comedy is not necessary.
Food, water, shelter and clothing are necessary for survival. Comedy? No. Music? No.
This is going by the literal definition. Now, I understand that life would be dull, moderately depressing, and uninteresting without entertainment, but we can all live without it. (I'd rather not, though, as I'm sure many would agree)
There may be some scientific study somewhere on the importance or health benefits of laughter, but, I'm sure we can survive without it.
Sorry for being too literal, but it's the truth...