"No-one can substantiate the 3,500 supposed victims."
Nobody can deny them either - the Israeli bulldozers made sure of that
So Ellen Siegel, Robert Fisk, the McBride Commission all the survivors who gave evidence - were all part of a Lebanese plot?
That took longer than it should to emerge.   
"Jim Carroll produces reams of paperwork"
And you have produced not a single scrap - all personal, agenda-driven opinion.
"he presents them as "eye-witness" testimony."
Yet another lie to add to the list
Please produce one scrap of evidence I have produced and claimed as "an eye witness account" that wasn't - waste of time asking for this, of course.
In fact I have avoided most eye witness accounts as they are not as readily available as the researched reports that were based on interviews.
While you are at it, you might produce an alternative account of the massacre that is not personal opinion or the official line put out by the perpetrators
Jim Carroll

SOME EYE-WITNESS ACCOUNTS HERE - all lies of course!!
"On Thursday, there was shelling when the Israelis came, then it got worse so we went down into the shelter. (…) We learned on Friday that there had been a massacre. I went to my neighbours' house. I saw our neighbour Mustapha Al Habarat; he was injured and lying in a bath of his own blood. His wife and children were dead. We took him to the Gaza hospital and then we fled. When things had calmed down, I came back and searched for my daughter and my husband for four days. I spent four days looking for them through all the dead bodies. I found Zeinab dead, her face burnt. Her husband had been cut in two and had no head. I took them and buried them. Samiha Abbas Hijazi (3)

".. they had put the men on one side and the women on the other… The armed men ordered us to walk in front, and the men behind. We walked like this until we got to the communal grave. There, the bulldozer started digging. Among us was a man who was wearing a white nurse's shirt; they called him and filled him with bullets in front of everyone. The women started screaming. The Israelis posted in front of the Kuwaiti embassy and in front of the Rihab station requested through loudspeakers that we be handed over to them. That's how we found ourselves in their hands. They took us to the Sports Centre, and the men were supposed to walk behind us. But they took the men's shirts off and started blindfolding them. At the Sports Centre, the Israelis submitted the young people to an interrogation, and the Phalangists delivered 200 people to them. And that's how neither my husband nor my sister's husband ever came back." Sana Mahmoud Sersawi (3)

… some Israelis and some Phalangists… placed us against the wall and … shot at the men. I was hit and I pretended to be dead. Three or four others fell on top of me. They were dead…. They then resumed their task, 5 or 6 times. They fired more shots to make sure that everyone was dead. At about five in the morning… I heard an Israeli on a microphone saying, "Give up your weapons, you will have your lives spared and those of your family." I tried to climb up the slope in order to give myself up like they said… I looked and I saw them placing the men on one side and the women on the other. Then I saw them shooting them. That's why I went back to hide… I stayed there until the evening. They were sitting around a table drinking alcohol, there was only a wall separating me from them. The wall was cracked; I could see what was happening. They were saying to each other, "don't leave anything that moves." Hamad Mohammed Shamas (3)

"The Israeli Army surrounded the camps, providing the murderers with all the support, aid and facilities necessary for them to carry out their appalling crime. They supplied them with bulldozers and with the necessary pictures and maps. In addition, they set off incandescent bombs in the air in order to turn night into day so that none of the Palestinians would be able to escape death's grip. And those who did flee – women, children and the elderly – were brought back inside the camps by Israeli soldiers to face their destiny."

"What will always stick in my memory is of a little boy that had come from the camps & his little body had no limbs. I can remember just holding him, holding his little body close. He was covered with blood and the life was running out of him. He was crying for his mother..They had also bulldozed buildings with people still inside, families still watching television, or having dinner. They bulldozed these people. They massacred these people. I saw bodies, piles of bodies, heaped up, mutilated & believe me they hadn't been shot. It was like a scene from what I would have imagined happened in WWII to the Jews. They had been executed. Children, women, animals, anything that moved-they had massacred…It was horror in there, it was horror. The stench, the massacre. They are war crimes. But I shall certainly never forget. Of all the horrors & atrocities & of the many things that have happened to me when I was in Beirut, nothing can come close to what I witnessed in these camps. Nothing." Deborah Thornton-Jackson (4)

"At noon on Friday, the second day of the terrorist massacre, and with the approval of the Israeli Army, the kata'ib forces began receiving more ammunition, while the forces which had been in the camps were replaced by other, "fresh" forces."

One of the journalists who went into the camps after the massacre reports what he saw, saying, "The corpses of the Palestinians had been thrown among the rubble that remained of the Shatila camp. It was impossible to know exactly how many victims there were, but there had to be more than 1,000 dead. Some of the men who had been executed had been lined up in front of a wall, and bulldozers had been used in an attempt to bury the bodies and cover up the aftermath of the massacre.