Our society has been rapidly becoming more partisan and the views of opposing political groups is veering off into caricature rather than any real understanding. Unfortunately our political system is easily gamed by simply attacking your opponent - rather than advocating for yourself and it has always been easier to vilify than constructively argue. When your political landscape can be neatly divided into two parts nobody needs to compete on ideas or policy and can instead get ahead by pushing their opponent down - in a more healthy multi-party system attack ads are (generally) viewed negatively by voters who can select a different similarly aligned candidate that hasn't been dirtied by getting in the muck so attack ads need to be used very deliberately when the impact will be high and, especially, when the attack is essentially unimpeachable[1].

1. i.e. if you have a video of your opponent clearly handing out a bribe to a judge you can simply start an investigation into their ethical conduct at a politically convenient juncture and most voters won't view the action as being politically motivated.