Using chemical weapons against the Iraqi Kurds.
Didn't this happen in 1989 (not sure about the exact year, could be '8? There wasn't a war movement then, right?
Palestinian suicide bombers blowing up buses in Israel.
Palestinian children being killed in Israeli "target" attacks.
If peace were established, these incidents (although, I wonder if these count legally as atrocities) would stop.
I suppose the peace camp would suggest that both sides restrain themselves and return to the table. I think, however, right now, there is a feeling that the peace process is dead. Also, the backing for the withdrawal plan by the U.S. probably will not be accepteable to the Palestinians.
I would add that there is no war alternative where this particular conflict is concerned, so (political & economic) pressure and intermediaries might have to be applied.