Life is hard. Bread is hard. Weather is hard. Music is hard. Like a stone, not like 'it's difficult'.
But it's not (always) agressive, at least not like i.e. gansta rap is. The biggest metal festival in here (Tuska) has had the least amount of incidents requiring police for several years in a row and metalheads are generally speaking one of the nicest people you'll ever meet. And the most incidents has generally been at Tangomarkkinat, so one could say that heavy music is actually good for your mental health, or at least better than traditional music.