NYC government has a particular moral ideology and they don't like that SA performs such an important function (caring for the poor that NYC neglects) in their city without buckling to their moral agenda. They would spend the lives of tens of thousands of impoverished citizens if they could force SA into a more palatable theology.
NYC went after them several years ago for exercising their right to refuse to employ openly gay clergy. They wanted to close down SA in NYC despite that SA provided a huge portion of shelters and other homelessness relief (something like 60% by some measure IIRC). And they wanted to pin the blame on SA ("We can't believe you'd force us to shut you down and let all our poor people starve!") when it was clearly their prerogative. They only changed their minds when it became apparent that they would lose the PR battle.
Around that time, someone started a "Let's hate on SA for being homophobic" thread on Reddit, but so many formerly poor people from all over the country (including many LGBT) came forward with their stories of how the SA saved their family from poverty; none of the first hand accounts corroborated the "SA is homophobic" narrative.
If you truly care about social justice, you support SA because they are clearly doing more good than any similar organization in the US; everything else is just social justice fashion.
1. PDF: http://www1.nyc.gov/assets/cchr/downloads/pdf/press-releases...