I actually agree that Obama is under no moral obligation to provide any financial assistance to his half-brother, whether Obama knew him or not. That said, Obama's lack of concern does make him a look like a hypocrite in the face of (1) his own personal wealth (2) his own repeated insistence that "the rich" should be compelled by the state to help those in need, notwithstanding the fact that his own relative(s) living on a dollar a month (!) has yet to receive any such help from him.
This supposed relative is only living on such a small amount because he is Kenyan. He is no exception among Kenyans.
If he were American, he would be benefitting from those social programs that Obama champions. As to Obama's supposed lack of compassion, this person may be a relative by blood but it's clear they don't consider themselves 'relatives' in the sense of real family. It's clear Obama's father didn't even consider himself a real father to Obama, or else he would have been present in Obama's life after the second year, but hey, doesn't matter "relative" is "relative" right? Obama must chase down his blood to the ends of the earth even if they mean nothing to him nor him to them.
In any case, social programs are fundamentally different from charity. The former is an entitlement written into the social compact, whereas the latter is a private benefit that can be withdrawn at any time. The former is far more valuable because while entitlements may be withdrawn by law, they are not dependent on the capricious whims of one individual and the recipient's relationship to them.
The most mysterious parts of Obama's life all occurred before he reached the age of 10, and as this story shows, his biological father has definitely had a limited impact on shaping who he is.