The Palestro massacre shifted French public opinion toward negotiating peace. [causal]
In another direction, however, Palestro proved a net, long-term gain for the F.L.N.; it brought home to France for the first time, and more sharply than anything else could, the cruel realities of the Algerian war, and in doing so strengthened the hand of those few then arguing for a negotiated peace.
Horne, Alistair, A Savage War of Peace- Alge…, loc. 472