Why not? That's exactly what liberals do today regarding the southern states...that their past is perfectly indicative of the present. That rationale cuts both ways.
The modern south is mixed, but the difference is that there's still a significant strain of racism in the south that's tolerated and sometimes even endorsed by its white community (see: the opposition to removing Confederate statues). I'd like to see you cite any significant strain of racism among modern Democrats that isn't immediately condemned. The south is getting better; but the reality is that it's considerably more problematic than the Democrats.
Besides, I'm still trying to grapple with how you can keep parroting the false "modern Democrats are racist" narrative when this is the party that successfully elected a two-term black president and has legendary civil rights leaders (like John Lewis) actively serving in office. Not that there aren't non-white Republicans, but it's definitely not the party you choose if you value cultural diversity and acceptance.