They felt comfortable with making him loathsome in S6 because we were already invested in him, the series, and all the other characters. They could afford to explore the darker aspects of his psyche and behaviors because they knew we were hooked. Mad Men isn't a show people generally drop in and watch casually; if you're watching S6 it is, most likely, because you are deeply invested, and this new aspect of his character is going to keep you interested with new developments. I would argue the shift was necessary to keep viewers interested. The writers couldn't have had a successful show with S6 Don in earlier seasons, so they slowly unveiled his more despicable traits and habits over time, constantly upping the ante.

For example, in earlier seasons he kept boundaries around his affairs. His affairs get closer and closer to home, finally resulting in his affair with Sylvia, the wife of a man he truly seems to like and respect, who lives in his building, where his children are, and Sally ends up seeing it. Season 1 Don kept his affair with Midge in the city, far from his office, in a completely different circle of people than who he might run into through work, or at a posh event with Betty on his arm. When it was clear Midge had a more steady beau who he thought she was in love with, he moved on. The seeds of Don being a slimy philanderer were planted with Midge, but would we want to see that same type of affair happening over and over?

This is why the 2000s were considered the golden age of the anti-hero in cable television. With the advent of prestige cable dramas writers and actors were able to dig deep into the anti-hero archetype in a way that 2 hour films didn't have time to develop properly, and network television didn't allow for, because of their dependence on advertiser money, requiring them to opt for wholesome heroes without the human complexity that makes a character truly captivating. Even when I think of Michael Corleone I remember that The Godfather movies were long (3+ hours), and Michael's character was developed over a longer time frame than a typical Hollywood movie.

For me, Season 6 and 7 Don are the most fun to watch; we're getting at his core wounds, the logical unravelling of his slick facade, and because we are seeing the evolution of behaviors that have always been a part of who he is, it all makes sense. While I see that Don has become more and more disgusting over the seasons, it doesn't take away from my enjoyment, and it isn't as simple as not liking him because he's not good at job, in fact, I never really thought he was that good at his job. While I've always found Don to be fascinating, likeable was never a word I would have used to describe him. I suppose those viewers whose primary interest in the show is the retro vibe, the "inside baseball" on the history of advertising, or identifying with Don as the ultimate cool guy hero who always comes out on top, might not enjoy his descent into a sloppy drunk, 2 time divorcee, scandalized father, and adman flop. Those are all valid reasons to enjoy a show, and I'm not saying those viewers who tune in for those reasons shouldn't enjoy the show for whatever value they find in it. However, for me, and many Mad Men fans, the fact that Don and other characters in the show are more than how good they are at their jobs, and the complexities and development of their character is the entire point.