I'm sorry, but you're wrong about the fact that "the Confederate flag flyers are unreachable".  The Democratic party's whole modern success strategy in the South has been to build a coalition between the local African-American population, the growing Latino population, and poor whites-- many of whom do fly the Confederate flag.  As distasteful as it is, a lot of the people flying it don't understand (or openly deny) the racist connotations of it.  They think it stands for rebellion, for identity, or for a jab against "PC culture".  Again, that interpretation is stupid and wrong, but it's widespread.

Now you're RIGHT that some people are incredibly economically racist.  And you're right that all of these people are unreachable.  But not everyone who calls up the mythology of the rebel flag-- especially in something as minor as a bumper sticker-- is a member of that population  is to lump a lot of undeserved people into the group.  That would foolishly mean giving up on trying for a great number of winnable votes.

And before anyone goes insane saying "what do YOU know about the South, Chicago boy", please keep in mind that I grew up in conservative Central Florida.  Florida's Democratic party had a coalition including poor whites for quite some time, in fact you could make a case that they formed more of a basis for Lawton Chiles long reign as Governor than other minorities did.  They turned out well to support Bob Graham and Bill Nelson, and made sure that McBride got the Democratic gubernatorial nomination over Janet Reno.  And yeah, my high school parking lot had its fair share of Confederate flag emblems, but I know for a fact that a number of those guys ended up voting for Al Gore over George W. Bush.