Gunmen chased fleeing revellers across the desert, shooting and snatching people

They moved people off the battle field and kept them hostage, yes. They did not target and shoot civilians, the IDF put the ravers in crossfire when they engaged the Palestinian resistance. There's plenty of footage of the incident online, and none of it shows that. I'd be happy to be proven wrong; show me evidence. If all you have is "trust me bro" from the Israeli government and media, who have a proven track record of lying (and already admitted that they lied about this latest Hamas operation), then your claims are to be ignored.