Think Al Sharpton will get out on the street with Alveda King to protest the real genocide of black children in this country?
For instance, I have read articles by several disability rights people who are "generally" pro-abort but are opposed to search-and-destroy missions against Downs and other disabled babies; feminist pro-aborts who think sex selection abortion (against female babies) is immoral; and of course there are FReepers amongst us who find it particularly offensive that 50,000,000 American babies have been killed in the last 35 years.
Perhaps some Americans wouldn't be too upset about the murder of unborn Muslim babies in Egypt, which has an abortion rate almost exactly equal to ours in the USA. But it's only natural to care for "your own" first and most.
In any case, I think it's legitimate to address people constructively by appealing to their most compassionate and protective instincts. If people are already pro-gay, you talk about how awful it would be if (hypothetically) genetically pre-gay babies were hunted down and killed before birth. If people are highly sensitive to racism, you talk about the grossly disproportionate number of black babies being killed. Start where they're at.
Eventually our hearts and minds may get stretched to the point where we care about every human life. We can only hope.