TV probably isn't your best source of information about the state of your society. TV has a fairly well-proven track record of focusing on a small amount of sensational cases rather than giving audiences the bigger, but less sensational, picture. how many psychos have you, your family and friends personally encountered in your day-to-day lives?
the nutjobs that you do have in the US (i would imagine you don't have that many more than other developed nations) are probably motivated by the same things as the nutjobs in other developed countries. they're politically, socially and/or economically disenfranchised and they're not sure how to deal with this, so they either find someone to blame (e.g. immigrants or 'degenerates') or they take the pussy's way out and go down in the biggest ball of flames they can (e.g. the batman guy).