It isn't about anger. Denial of the media isn't going to suppress ISIS actions or 'rile' them any further. They are committing war crimes freely and putting forth this public effort so that the US will intervene against them, and turn a tide of war in their favor. They have the money and the weaponry, and that would bring the support.
It is a shame what happened to all the innocent journalists, and a tragedy this kind of barbaric brutality goes on in the world still. His death will pass but we couldn't and wouldn't have saved him. The US does not negotiate with terrorists.