Why Is Dixie Named Dixie?

The issue's not yet signed and sealed.
Three cogent answers hold the field,
and no-one knows which is the best.
I'll set them out before you, lest
the question go a-begging.
First
(and this one's frequently rehearsed,
but holds least clout - at least with me),
the Mason-Dixon Line must be
the great divide: South, slavery,
North, freedom. Dixon, Dixie - see?
The trouble is that way back when
those two unstinting Englishmen
surveyed the Line, none under heaven
(we're talking seventeen sixty-seven)
could care a cuss if blacks were pressed
to toil unpaid at whites' behest.
And Delaware, by no means least
of slaving states, lies north and east
of said divide.
Manhattan, now:
though it may try to disavow
a past that wasn't quite PC,
New York had sloughs of slavery.
A Mister Dixie held some lands
(right where the Guggenheim now stands):
the human property he owned
led folks to talk of "Dixie's Zone"
whenever slaves were being mentioned,
and gradually, by extension,
this came to mean the South. Could be.
Pursuing perspicuity
is noble in itself, and so
I offer as my final throw
the one which really should have won
(who measures merit, though, by fun?)
Louisiana, sovereign state,
sought (sensibly) to circulate
its very own banknotes. Problem was,
the Cajun cash collapsed, because
nobody trusted it. Each bill
was written in (for good or ill)
official French, so - quelle caprice! -
each sawbuck said, not ten, but "dix".
Thus, Dixie's fixed in every brain
as something quaint, quixotic, vain.