You present a nice story and make it very personal. However, you don't give your name. So, there isn't much substance to it.
By the way,
Your story tells enough to validate the Arab story when you talk about 'inexperienced' soldiers going door to door tossing in grenades and spraying with rifle fire [in a civilian residential community]. Your speaker pointed out that Deir Yassin was located strategically. This is a military assessment. The occupation of the town was a military objective, as was the terrorizing of the Arab populace.
Could it be that you were ashamed when you were present at the event because you saw it directly. But, later, the grand talk in Oxford gave you a way to be free of that shame, and so you took it. This is how all of us remain complicit in the Iraq occupation, and, I know you hate to hear it, but it is how the German people were brought in by the Nazis. When governments do evil, they tell you it is in your best interest, in fact, it is necessary for your survival, and, well the victims were bad people anyway.
But the question is, have 60 years of war really been in the best interest of the people of Israel?
Is unending conflict with their Arab neighbors and the destruction of the Palestinians in Gaza and the West Bank really their only hope of 'survival'?
Could there have been, and could there be now, a better diplomatic policy for Israel than military supremacy?