As described in the post above, BC failed to demonstrate a grasp of basic logic in his statement and thus deserves no credibility regarding his claim. This happens quite often with BC, and he is therefore not to be taken seriously.
What it does demonstrate is apparent reading comprehension problems on your part.
bc did not say that "all Democrats are racist." He said that the
Democratic party is a racist institution (which is patently demonstrable). This is what he actually said:
The organization that is racism is the Democratic Party. And since it's not possible for a good Mormon to be a Democrat, it is also not possible for a good Mormon to be racist.
Hence, if you want to put this argument in standard form, it would be:
The Democratic party is racist.
No faithful Mormon can be a Democrat.
Therefore, no good Mormon can be a racist.
If the first proposition is assumed to be true, and if the second proposition is assumed to be true, then the conclusion does not follow from the first two premises. It is not a valid deductive argument. Now, if bc had said what you ascribed to him, which was that all Democrats, not just the party (which leaves open the possibility that any number of individual Democrats are not racists) are racists. Then you would have:
All Democrats are racist.
No faithful Mormon can be a Democrat.
Therefore, no good Mormon can be a racist.
This is still not a valid deductive argument, as the premises still don't follow necessarily from the conclusion (just because a Mormon is not a Democrat, doesn't mean that he's not a racist).
There are a number of very good reasons why no good, faithful Mormon could ever be a racist (doctrinal reasons), but simply not being a Democrat is not one of them (there are a plethora of other reasons why active support and participation within that party would be spiritually and doctrinally problematic).
I'll have to call bc on this one as a matter of formal logic, but I understand what he was trying to say. Basically, it boils down to this: the core of the Democratic party's politics and political ideology is class war and identity politics. Identity politics is a central aspect of the party's hold on power and its divide and rule strategy between ethnic and racial groups and between legal and illegal residents. No LDS who understands and takes his Church seriously could be a part of such an institution.
One of the reasons I am no longer a Republican is precisely because that party has become, itself, too unprincipled for me to remain officially associated with.