I'm somewhat conflicted about this issue, largely because one of the photographer's defenders claimed that the photos had in fact inspired some viewers to provide some type of aid or assistance to the homeless (if those people actually photographed received any of this aid is uncertain, as is the veracity of such claim that aid was provided).
Otherwise, in this case, there is a fine line between exploitation and documentation. The photographs are very good, this is not someone who took a couple shots of homeless folks for some instant drama. On the other hand, as shadowfax noted, or to which he at least alluded, the photographer possibly has a good chunk of his ego invested in the project. Yet, in fairness, I would have to know the guy before proclaiming this assumption to be truth.
Generally, ego and art (however you want to define it) are inseparable, so I don't begrudge photographers, painters, authors, or musicians who indulge in some self-gratification. Yet, in this particular case, if the ego is being stroked, it is being done so at the expense of people in very dour conditions, conditions that provided the photographer the drama from which to work and, subsequently, receive praise.
This, then, leads back to my ambivalence. If these photos actually provide some amount of succor to the homeless, then irrespective of the photographer's motive, fine, keep shooting away. If not, though, then there is a possible degree of exploitation and objectification that is arguably worthy of some scrutiny. And if someone doesn't really care if it is exploitive or not, that is probably fine too, I'm just not politically correct enough to proselytize. Yet, if someone does care, then I think they have good reason to at least debate the issue.
Where I am not ambivalent is in the nausea that overcame me while reading excessively trite or outright pretentious arguments in support of the photographer. As one person commented, most of these folks would cross the street, holding tightly on to their personal belongings, if they actually came across some of the people photographed. If they want to stimulate their passions and expand the depths of humane understanding, then they should go out and meet these folks without relying on artistic enhancements to facilitate a reaction. Otherwise, it's all pretty ephemeral, isn't it?