Q:
We are frequently asked, "Why did Israel attack?"

A:
Israel's motive is irrelevant. They did it. They admit they did it. If motive were a factor, then Charles Manson should be released from prison because no one knows his precise motive for mass murder.
Q:
Still, they must have has some reason to attack. What plausible motive could they have had?

A:
We were an intelligence ship and the Israelis were doing something that they did not want the US to know about. One popular writer of Jewish fear-literature, John Loftus, writes in "The Secret War Against the Jews" (a Jewish version of The Turner Diaries) that Israel attacked deliberately because Israeli authorities believed that USS Liberty was relaying Israeli war plans to Egypt in order to assure the destruction of the Jewish State. That is patently ridiculous, but widely accepted even in Israel. Loftus claims to have documented his position through interviews with long lists of "retired old spies" whom he refuses to identify. While Loftus may be correct about Israeli paranoia, he is totally wrong about Liberty's mission. Liberty's primary mission was to collect intelligence on the Soviet forces in the area. The ship didn't even have a qualified Hebrew linguist aboard.
Q:
What other reason might they have had for attacking?

A:
Intelligence analysts agree that they attacked because they feared we might learn something that they did not want the United States to know.

That could have been

1. The planned invasion of the Golan Heights which was set to start a few hours after Liberty's arrival in the area. When Liberty arrived, the invasion was postponed for 24 hours, Liberty was attacked, and the invasion took place the next day. Did they postpone the invasion until Liberty was out of the way and unable to report on the war?

2. It is possible that they were afraid that Liberty might learn and report to the United States that Israeli forces were executing up to 1,000 Egyptian Prisoners of War at El Arish at the very moment that Liberty was just 13 miles off shore.

3. It is also possible that USS Liberty was attacked to prevent the ship from reporting a deliberate massacre of 14 Indian United Nations peacekeepers that took place in Gaza shortly before Israel's attack on USS Liberty.
Q:
Some of those reasons sound far fetched. Is there any proof to substantiate them?

A:
Israeli apologists dismiss these stories as untrue or wildly speculative, despite the fact that they are well documented. Israeli apologist-historian Michael Oren in his book "Six Days of War" and in published articles dismisses the claim as untrue claiming that, if it were true, there would be mass graves, reports in the major media, and great outcries from Egypt for justice.

Behold! There are mass graves, major media reports and cries for justice.

Attention is invited to

CNN reporting on the subject which reports the mass graves of POWs and a TIME Magazine story which reports the outcry

More on the atrocities can be found in Jim Ennes's report in The Washington Report on Middle East Affairs, and in Jim Bamford's Body of Secrets.