In your opinion, how are leftism and socialism different? In what way are black Americans socially conservative? That community has an illegitimacy rate of over 70%. What is so socially conservative about young women being knocked up out of wedlock by different baby daddies who are nothing more that sperm donors? How is being on the dole socially conservative?
Maybe I'm totally wrong about this, but I think leftism implies universalism rather than the "us vs. them" / tribalism / racialism seen in mainstream black culture. I agree that the typical lifestyle of the black community could not be called socially conservative. But you do see a lot of socially conservative / socially backward tendencies nonetheless. Remember Prop 8 to ban gay marriage in California?
"Whites voted very narrowly against the ban, 51-49 percent. Asian-Americans voted the same. Hispanics voted for it, by 53-47 percent. Blacks voted for it, overwhelmingly, 70-30. Blacks can be said to have put it over the top. Hypothetically, had no blacks voted, we compute a vote of 50-50," according to an analysis by ABC News Polling Director Gary Langer.
So you see, I don't think the majority of Blacks and Hispanics like to have to back a candidate who supports gay marriage. It must be a "necessary evil" / "end justifies the means" kind of thing for them.