This is a decent article and several other people have hit on the core idea here, which is normalization of repulsive far-right ideas, not necessarily demonization of the left.
For many decades (or even centuries), cultural conservatives were obsessed with turning back the clock on social progress. Racial segregation, blocking gay marriage, etc. But in this modern, hyper-connected internet era, many of them are realizing that they can't win that fight. They have given up.
Instead, their new focus is on trying to normalize their own repellent views by suggesting they are "just like everyone else." There are two types of propaganda: there's the type where you insist your views are superior to all others ("Whites are better than blacks"), and then there's the type where you insist your views are just as normal as all others ("White identity and black identity politics are the same thing"). This type of propaganda is extremely hard to fight because any opposition makes it seem, to moderate white observers, like you're being bigoted ("anti-white racism"), which in turn causes those moderate whites to slowly become radicalized too ("Hey wait, why isn't there a White History Month? This guy makes a good point!"). Over the last decade, as whites have slowly lost more and more of their political and cultural power, we have seen this type of white identity politics become increasingly popular, culminating with Donald Trump, who ran essentially entirely on a platform of white identity grievance politics.
When you argue with Trump supporters -- not just regular Republicans, but the really vile, dyed-in-the-wool Trumpers -- you'll notice that they rarely make any effort to defend Trump himself or his actions, or the actions of white supremacists. Instead, they immediately deflect blame by suggesting some other group on the other side (usually Hillary Clinton, the DNC, Black Lives Matter, etc) is doing the same thing, or something similar. In other words, their politics revolves entirely around a basic assumption that everyone in the world is just as disgusting and hateful as they are. You see this manifest time and again in their cynical insistence that any person who supports any sort of cause or issue is "virtue signaling" or participating in some kind of scam, their bitter anger at any demographic group that embraces their heritage and culture. They are angry, bitter, cynical people who are ugly and rotten on the inside, and they know it. They have no illusions about it. They have lost all interest in improving the world and instead, simply want to watch it burn down around them. In their minds, the best case scenario is that the world is rebuilt stronger and whiter than before. The worst case scenario is that they die, but everyone dies eventually anyway and these people have given up all hope and no longer care about their own self-interest.
To borrow a line from The Dark Knight: their goal is to prove that deep down, everyone is as ugly as them.
They are people who have given up on life and are filled with anger and resentment when they see others succeeding. Roseanne is designed to make them seem sympathetic, to make their views and ideas seem understandable, just as so many dozens of thinkpieces since November 2016 have been designed to help us coastal liberal elites get into the mindset of the poor, downtrodden Trump voter. And the strategy works; just look at how many fence-sitters on this very forum regularly piss their pants at the slightest suggestion that the views expressed by Trump's supporters are abhorrent and should be condemned. "It's just another opinion and you have to respect them! How dare you suggest Trump voters are all racists! They're just normal, cuddly working-class people like anyone else!"
Normalization of disturbing views is their goal. Asserting their superiority comes later. If Roseanne came blaring out of the gate with overtly homophobic or racist storylines, the show would have been cancelled or never even made it to the airwaves. Roseanne knows this. The goal is to normalize her white identity views, alongside other media and other political platforms designed to normalize white identity, so that eventually they can replace white identity with white supremacy and begin to truly roll the clock back. It's about playing the long game.
