It is not disputed that a Muslim militia carried out a massacre later in those camps.
Why no outrage about that Jim?
Is it only a massacre if Jews can be accused?

From Wiki
On May 19, 1985, heavy fighting erupted between Amal and Palestinian camp militias for the control of the Sabra, Shatila and Burj el-Barajneh camps in Beirut. Amal was supported by the predominantly Shiite Sixth Brigade of the Lebanese Army commanded by Major-General Abd al-Halim Kanj [1] and even by some units of the predominantly Christian Eighth Brigade loyal to General Michel Aoun stationed in East Beirut. Virtually all the houses in the camps were reduced to rubble.

In Shatila, the Palestinians only retained the part of the camp centered around the mosque. Burj al-Barajneh remained under siege as Amal prevented supplies from entering or its population from leaving. The death toll remains uncertain, but is likely to have been high.