I think the intention of the war photographers is not to persuade the politicans that the war too horrific to fight and should be abandoned, but to persuade politicans that the consequences of not acting in the war are far too grave for the innocent people that suffer them.
Seems to me they are doing a pretty good job, considering that the governments are keeping at it, even though general public opposes.
I suppose the effect in the western world is limited, but in the countries where these pictures are shot they sometimes are the first truly free press actions in decades and that means a lot.