Happy and sad endings.

I've recently finished up with Cry Havoc, my two-act political thriller in The Blue Room Theatre. One of my friends came and saw the show, and while loving it a great deal she asked if for my next playscript I could write "something a bit more uplifting". I half-jokingly replied that uplifting isn't something I generally do. I like dark material. I enjoy putting my characters through emotional torture. In the three main dramatic works I've had staged (and this is spoiler territory, in case you're worried) I've killed a President and brought down his government in one play, shot one character dead and traumatised the other in a second, and revealed everyone was dead all along in the third. Happy uplifting endings is not what I do. The reason I'm writing about this is because at a party on the weekend a writer friend of mine commented that the reason for this is that depressing endings are easy. She figures happy endings are much, much harder. This surprised me, because I've always found happy endings to be much more simplistic and trite than unhappy ones. It did get me thinking, however. What do you think? Is it easier to write a happier ending or a sad one?