Personally, I don't think it's possible for the Democratic Party to effectively disavow every online crank and stupid editorial that gets published that the right uses to damage the party's brand, primarily when most of that stuff is published just for the reason of getting the reaction it gets. It's just an endless vicious cycle.
If people are looking for a reason to hate Democrats, they'll find it regardless.
The rest of us need to be better microphones for the good things Democrats do.