I don't know about the intricacies of their relationship as I haven't seen the rest of the series and so was basing my intrepretation off the final video. It's a nice moment, but I'm sure there's a decent eight years lead in that I've missed - and will go back to.
I don't think that anyone should change their stance on the Confederacy, because it means different things to different people.... and in the UK we have a similar debate about what it means to be British in light of the British Empire. I happen to think that the most racist instittution in the UK is the British Monarchy - but lots of people disagree with me. Including for some reason lots of progressive POC. It seems counter intuitive, but that's just how it is.
When you ask British people to consider the Monarchy in light of all the horrible things they have done through history, the backlash is overwhelming. As with Confederacy, I imagine it's baked into their identity. People are often incapable of re-evaluating their histories when they hold a strong sentimental attachment to it, when it has become an integral part of how they represent themselves in the world and when they love people who belong to that world. That's the justification and you're right, the objecion still stands. "The Queen has been an excellent head of state for the UK" doesn't excuse 1000 years of Empire and warmongering against your own population and everyone else - but it sets the tone for how well the discussion is going to go.
Those people will never be won over. Their stance will never change because of the emotional distance required to travel and what they hold dearest to them. Is there a mid place between the Confederacy (politcal) and growing up a confederate (social)? It's a complex question with no easy answer. Is Blanche an evil person? Or is she just a person raised with some maladaptive thought processes due to her environment. In most echo chambers she's the former - for any progress to be made and filtered into the next generation she has to be considered the latter. The best we can likely hope for is what happened in this fictional relationship. The merging of subjective narratives and a mutual understanding and respect.
I also think this fictional relationship is telling. These two characters get on despite their obvious differences. Roland has jokes, but in the extract I saw at least, he was never THE Joke. Blanche is cast as the figure of fun for her outdated views. That certainly seemed to be the case when Bea Arthur was talking to her about her Jewish heritage. I imagine that was the intention of the writers. The fading Southern Belle. She's out of step with a changing world and it's catching up with her. I'm not sure it would get on TV at the moment and that's a shame becaus, to my mind at least, it's brilliant satire and very beautifully handled. I'll watch more and get back to you.