I prefer to listen to music in which one has to work towards its full comprehension. "Positive" music by the contemporary definition seems to be the stuff that folks bask in passively, whether it be the Beatles during a quiet, neighborhood barbeque, or whatever stuff my peers listen to during partys nowadays. The same principle applies: let it do its work in the background, like a conniving call girl on your boss's balls mid-afternoons every Thursday. (Yet you wonder why you didn't get that pay raise last quarter?)
Metal and classical music require quite a bit of engagement, and it doesn't afford the same carefree atmosphere that so-called "positive" music does. Because it demands our attention in a society that prides itself in freedom of choice--and most folks prefer not to be faced with more profound levels of reality during their experience--these two artforms are considered intrusive and offensive by many. Note also, that popular music functions equally, if not moreso, on radiating outwards and initiating social contact as it does on engaging dialogue with the listener.