Everyone there is damaged in some way and looking to cover it. The ones smiling and hedonistically taking pleasure in the moment are empty and soulless, looking to fill the void in an ineffective way, numbing the pain rather than treating the symptom. The ones who hate it and clearly don't fit there are dissatisfied with life and are trying whatever they can - what people are "supposed" to enjoy.
I suppose a small fraction could be infrequent club goers who are generally satisfied and somewhat ironically indulging, but they likely came with a group they will stick with rather than seeking hook ups and are still probably reaching for some thrill they feel they failed to satisfy.