Cheerfulness is a choice IMHO. And I choose to be happy, cheerful & pleasant whenever I can. That is most of the time. I battle depression and have learned that I can keep it under control by positive thoughts, cheerful choices & kindness. And I count my blessings many times throughout the day. So no it is not illegal. Personally I think God wants us to be happy with all of the blessings he has blessed us with. Even bad or sad things that happen, there is always something to learn or gain. Sorry for mentioning my God but that is just me. Without him I could do nothing.