As Haaretz’s second Israel Conference on Peace approaches, one thing should be perfectly clear: The Israeli left, which has been out of power for all but 24 months of the past 20 years, needs a new agenda if it hopes to lead anytime in the foreseeable future.

For 20 years, leftist leaders have telegraphed a few consistent messages: the Oslo process could have led to a peace treaty but was cut short by the Rabin assassination, as Oslo architect Yossi Beilin has argued; the peace process collapsed because of extremists on both sides, with each side sharing equal culpability; the military occupation and civilian settlements are to blame because they provoke Palestinian violence.

Not that the left ignores Palestinian terror, but it contends that the occupation is the source of the violence against Israel, as if the Palestinians are not active agents in the conflict but rather purely reactive. Thus ending the occupation will end the violence.

These messages have utterly failed to resonate with the Israeli public, whose narrative is that Israel took its chance for peace and was rewarded with suicide bombings in the 1990s, the second intifada and three wars in Gaza. Now it sees no partner for peace, especially with the Palestinian areas divided between Fatah and Hamas, and does not trust the left to protect its interests.

Indeed, Oslo architect Yossi Beilin himself understood back in 1993 that Palestinian violence would annul progress that was then in train to lift the occupation: “When we are not there as occupiers, and there is no justification politically or whatever for the Palestinians to say: 'We are fighting against the occupiers', but it's their own people, it's a very different ballgameIf violence continues, if, God forbid, terrorism continues in the same dimensions in the coming months, before we talk about the permanent solution, I think that the failure of this agreement will be obvious.”

The left lost its credibility because Oslo's failure seemed obvious to everyone but the likes of Beilin and the peace camp.

'Leftist' need not be a dirty word. We must reestablish our principles and sharpen our message, so that they will be authentically leftist and consistent with what we demand of both the Palestinians and of ourselves. Those principles are that we are always prepared for peace and a just solution, but only with those who share our commitment to these goals and also hold themselves accountable for their actions.

Just because you can explain someone’s motivations and behavior, it doesn’t mean that behavior is justified. All parties should be held accountable for their actions. For all the centuries of oppression and humiliation Jews suffered, from the occasional massacre under Muslim rule and the Spanish Inquisition to the pogroms and the Holocaust, the Jewish people never engaged in terror en masse. Indeed, the last time our people tried the way of violence, doing so led to disaster in the Great Revolt in 70 C.E. and the Bar Kochva Revolt in 135. These failed uprisings, these Jewish intifadas, should serve as a cautionary tale to the fate of those who are committed to the violent overthrow of the occupiers.

However much we perceive the occupation to be nefarious and the settlements to be obstacles to peace, we cannot ignore that anti-Israel rhetoric does far more to thwart peace efforts. The anti-normalization campaign in Palestinian society is so strong that when the Israeli left talks about peace and reconciliation it ends up talking to itself.

Consider the cases of Mohammed Dajani, the Al-Quds professor who was forced to resign after taking a group of students to Auschwitz and Amira Hass, the Haaretz journalist asked to leave a Bir Zeit lecture by two Palestinian professors. If we cannot begin a discussion about peace and reconciliation, how are we supposed to get any further than the starting point?

Even worse, the Palestinian leadership has often qualified its terror condemnations, berating the violence for not serving its own national interests rather than being morally reprehensible, and has been deafeningly silent about the last wave of attacks as well as videos praising the murder of Jews.

These phenomena seep into the conscience of a frustrated Palestinian society as well as a wary Israeli public, which looks at the left’s willingness to take further risks for peace as defeatist or suicidally naive.

The Israeli left’s agenda, therefore, should be to convey a firm message of commitment to both our Palestinian partners and the Israeli people to the principle of being prepared for peace but not for peace without accountability and responsibility.

That principle requires a strategy by which we offer a threat and a promise, in the spirit of Thomas Schelling, the Nobel laureate who wrote of the strategy of conflict. When the right threatens not to negotiate if Palestinians engage in terror but offers no promise if they renounce terror, Palestinians gain nothing by switching strategies. Israel must make a credible threat but also an enticing promise.

To the Palestinians, we the principled Left say that we cannot help you until you take responsibility for your actions and get your own house in order. We want peace tomorrow but are unable to convince our public to pursue that path until it knows that the other side is equally committed. Netanyahu has declared that he believes that Israel will always live by the sword. We do not believe that is necessary, but are willing to do so if necessary. That is the threat. The promise is simple, a state in all the West Bank and Gaza.

To the Israeli public, we say that the settlement enterprise closes the door to any possible peaceful arrangement and comes at great cost to citizens who remain within the Green Line. Therefore, we must roll back this venture by dismantling all illegal outposts and ending all financial incentives over the Green Line, redirecting these funds for the benefit of those in need within Israel’s internationally recognized borders. We must also stress that we will not accede to a Palestinian state until the other side reins in terror, but that we cannot realistically expect the Palestinian security services to do our bidding without seeing that Israel is genuinely preparing for the eventuality of a two-state solution.

We have no control over the Palestinians, and may never see the day of peace. Israel’s left must therefore focus its efforts on regaining its own citizens’ confidence and saving Israel from further descent into its interdependence with the territories. 20 years ago the likes of far-right activists Daniella Weiss and Moshe Feiglin were the fringe, and the left was part of the mainstream. Today the opposite is true. Is this not sufficient evidence that we need a new agenda?

No tolerance for Palestinian violence and no tolerance for the settlement enterprise are one and the same principle. That is the principle of always being ready for true peace, where both sides take responsibility for their own actions.

Steven Klein is an editor at Haaretz and an adjunct professor at Tel Aviv University's International Program in Conflict Resolution and Mediation. Follow him on Twitter: @stevekhaaretz