Is having fun pointless?

It seems pointless to me. But perhaps disengaging the brain and allowing oneself to be spontaneous is what it's all about. But look what happens to large numbers of young people and even some older people when then disengage their brains in the name of fun. They go mad. They become wild. They go out of control. They do stupid things. They become anti-social, criminal and dangerous. They stop thinking about other people and do them harm. Isn't sponteneity dangerous. How can you relax and have fun and trust yourself not to do anything stupid? I saw some kids on the TV the other day playing and having fun. Their behaviour was random. chaotic, senseless, pointless purposeless (to me). It this what life is all about? Behaving with random sponeneity for 70 years and then dropping dead? Fun may feel good but I don't think that it achieves anything? Isn't life without achievement pointless? Is the answer to learn how to moderate fun and to switch it on and off at will? Help.