What he's saying is: many socially-driven businesses are pure BS. That doesn't mean he doesn't believe that a genuine socially-driven business can be built to solve that problem.
I think what the author means is that a lot of the businesses CLAIMING to be "socially driven" are pure BS, not that the very idea of a socially driven business is inherently BS.
That's an..'interesting' parsing of what he's saying. Is it just me or is it fairly apparent to most others that he's likely saying he's surprised that homelessness in general isn't being tackled (without speaking to the likelihood of success) by a startup, and he then follows by stating the obvious: that most startups who talk about 'changing the world' are blowing smoke. Of course, the unstated insinuation being that a startup aiming to reduce homelessness would actually be worthy of that title. Not sure why you jumped to the least generous interpretation possible but I'd bet a lot of money that there's no there there.
What he's saying is: many socially-driven businesses are pure BS. That doesn't mean he doesn't believe that a genuine socially-driven business can be built to solve that problem.