As a born and raised Republican, it has been a shame for me to watch the transformation of the party.  It is quite true that the party was founded on the principle of abolishing slavery, but the party has changed greatly in the last 150 years.

There is almost nothing left of what used to be called "Rockefeller Republicans".  The few still around seem to be isolated in the northeast part of the county and are referred to derogatorily as RINOs (Olympia Snow, Arlen Specter, Judd Gregg, Sue Collins).  On the other side, the influence of the old "Dixicrats" seems to be fading as well.  Strom Thurman did not change parties due to the Republican party's greater support of civl rights.

When Goldwater defeated Rockefeller in the 1964 primary, I think it signaled the beginning of the end of that section of the party as influential.  Nixon's use of the Southern strategy, although he presented himself as a moderate up here in the north pretty well finished it off.

I think the most compelling argument regarding the Republican party's current appeal to the black voter is the paltry numbers they get now.  I think it has been around 15% since Roosevelt in 1933.