Let's assume that the writer's intend the viewer to remain sympathetic with the main character. (I have not seen this show)
When chemistry teacher, Walter White, is diagnosed with Stage III
cancer and given only two years to live, he decides he has nothing to
lose. He lives with his wife and teenage son, who has cerebral palsy,
in New Mexico. Determined to ensure that his family will have a secure
future, White embarks on a career of drugs and crime. He proves to be
remarkably proficient in this new world as he begins manufacturing and
selling methamphetamine with one of his former students. The series
tracks the impacts of a fatal diagnosis on a regular hard working man
and explores how a fatal diagnosis affects his morality and transforms
him into a major player of the drug trade.
Another show which is also transgresses the social norm is Dexter. A show about a likeable serial killer. As he is killing villains who have escaped justice, he is a perverse hero; righting the wrongs within the legal system... (a problem for those countries and states which are anti-death penalty). This aside, the show presents the lowest of the low and evokes in the viewer a desire for revenge and the relief that there is a way to remove undesirables from our society; in doing so increasing our and our loved ones' safety.
Is it because it is a TV show and not real life?
Difference between TV and reality:
I can say, uncategorically, that within the context of real life these people would not be regarded as likeable.
As for the serial killer; real life doesn't give us black and white scenarios as the show does.
Why is this?
Fiction removes the factor's from the situation that cause an average person to lose sympathy for a person committing atrocities.
As for the show Breaking Bad, plays on the hard luck story of this man and his lofty plight to provide for his family. Yet, in reality he is destroying and damaging a huge number of lives. My guess (understanding human psychology and hollywood) is that the show would objectify or dehumanise the main character's victims and instead focus on the "greater good" that he is serving and his internal struggle.
Fiction carves reality out of the situation.
When confronted with the reality of a situation the feelings invoked in the viewer are very different.
See this Real life news story for an example of the real life consequences of methlabs.
Warning: graphic images Children are the silent and small victims of skyrocketing number of home meth labs
Warning: graphic images An image of a the teeth of a crystal meth addict with meth mouth.
Creating a sympathetic protagonist is an artform:
Your Hero: Top Ten Rules (Expanded)
List key features a writer needs to use to create a sympathetic protagonist needs. There is a basic agreement about the features a sympathetic protagonist needs to succeed within the writing world (any google search will show this).
Playing the Viewer like an Organ: Norman Bates as the Protagonist of Alfred Hitchcock’s Psycho
Psycho is a film where the director intentionally and obviously
manipulates the audience. In fact, Alfred Hitchcock took pride in his
manipulation of the viewing audience, remarking in an interview, “You
might say I was playing them, like an organ,” (Truffaut 269).
Hitchcock’s main intention in manipulating the audience throughout the
film is to make us complicit in the actions of Norman Bates.
The central shift of protagonist in Psycho is mostly an unconscious
one. By the time Marion Crane prepares to take a shower, the narrative
has already begun to follow Norman as much as Marion; after Marion
leaves the parlor, we see Norman go up to the mansion and sit at the
dinner table, waiting. We are unaware of the shift until Marion’s
narrative is abruptly and radically ended by her death in the shower.
By that point, the film belongs to Norman and Hitchcock is careful to
make us root for him.
It would seem that evoking audience sympathy with an "anti-social" protagonist, is an artform and the key to seeing why it is effective onscreen and not in real life lies, with an inspection of the key features writer's use to evoke feelings of empathy, maintain an audience bond with the character, by creating internal conflict, a heroic fighter, with care not to cross boundaries that will evoke revulsion in the viewer.
The question and answers at Sympathetic portrayal of an evil protagonist with good motivations explain this in more detail.
Breaking Bad IMDB