When you have been somewhere like that, forgetting it isn't an option. It is widely accepted that expression of negative emotions (through writing, art or even just talking to someone) is much more psychologically healthy than bottling them up - especially if you have suffered from a mental illness (as I believe Munch has). Just because you don't understand it, or it doesnt touch you personally, doesnt make it bad art. Just not the kind of art that you like.