In the Guardian article, Benny Morris (whose historic research I very much appreciate) says this:

"Neither can one avoid the standard Zionist rebuttal: "No war - no Palestinian refugee problem", meaning that the problem wasn't created by the Zionists but by the Arabs themselves, and stemmed directly from their violent assault on Israel. Had the Palestinians and the Arab states refrained from launching a war to destroy the emergent Jewish state, there would have been no refugees and none would exist today."

This kind of editorializing isn't one of his strengths. The fact is that the Arab forces were fighting only over land granted to the Palestinians in the partition plan. Israel has always had a policy to never fight any battles on Israeli land. Israel wasn't defending itself against the Arabs in the 1948 war. Quite the reverse is true. The Arabs were defending themselves against the Israelis in the 1948 war:

Statehood and Expulsion 1948

What was the Arab reaction to the announcement of the creation of the state of Israel?

"The armies of the Arab states entered the war immediately after the State of Israel was founded in May. Fighting continued, almost all of it within the territory assigned to the Palestinian state...About 700,000 Palestinians fled or were expelled in the 1948 conflict."

"The Arab League hastily called for its member countries to send regular army troops into Palestine. They were ordered to secure only the sections of Palestine given to the Arabs under the partition plan. But these regular armies were ill equipped and lacked any central command to coordinate their efforts...[Jordan's King Abdullah] promised [the Israelis and the British] that his troops, the Arab Legion, the only real fighting force among the Arab armies, would avoid fighting with Jewish settlements...Yet Western historians record this as the moment when the young state of Israel fought off "the overwhelming hordes' of five Arab countries. In reality, the Israeli offensive against the Palestinians intensified."

Benny Morris has changed his tone a bit on the Zionist leaders position on ehtnic cleansing. In some of his previous works he has this to say about it:

Ethnic cleansing - continued

"Following the outbreak of 1936, no mainstream (Zionist) leader was able to conceive of future coexistence without a clear physical separation between the two peoples - achievable only by transfer and expulsion. Publicly they all continued to speak of coexistence and to attribute the violence to a small minority of zealots and agitators. But this was merely a public pose..Ben Gurion summed up: 'With compulsory transfer we (would) have a vast area (for settlement)...I support compulsory transfer. I don't see anything immoral in it,'" Israel historian, Benny Morris, "Righteous Victims."

Ethnic cleansing - continued

"Ben-Gurion clearly wanted as few Arabs as possible to remain in the Jewish state. He hoped to see them flee. He said as much to his colleagues and aides in meetings in August, September and October [1948]. But no [general] expulsion policy was ever enunciated and Ben-Gurion always refrained from issuing clear or written expulsion orders; he preferred that his generals 'understand' what he wanted done. He wished to avoid going down in history as the 'great expeller' and he did not want the Israeli government to be implicated in a morally questionable policy...But while there was no 'expulsion policy', the July and October [1948] offensives were characterized by far more expulsions and, indeed, brutality towards Arab civilians than the first half of the war." Benny Morris, "The Birth of the Palestinian Refugee Problem, 1947-1949"

More on the subject of Zionist leaders and ethnic cleansing:

"Joseph Weitz was the director of the Jewish National Land Fund...On December 19, 1940, he wrote: 'It must be clear that there is no room for both peoples in this country...The Zionist enterprise so far...has been fine and good in its own time, and could do with 'land buying' - but this will not bring about the State of Israel; that must come all at once, in the manner of a Salvation (this is the secret of the Messianic idea); and there is no way besides transferring the Arabs from here to the neighboring countries, to transfer them all; except maybe for Bethlehem, Nazareth and Old Jerusalem, we must not leave a single village, not a single tribe'...There were literally hundreds of such statements made by Zionists."