Plan Dalet was not defensive.

As for the Jerusalem quarter, that's not comparable: no one was massacred, and the action followed a Zionist attempt to take land it was not entitled to.

Here's the relevant bit from https://en.wikipedia.org/wiki/Battle_for_Jerusalem:

On 14 May and the following days, the Etzioni and Harel brigades, supported by Irgun troops, launched several operations that aimed to take over the Arab side of the city. In the meantime, the Arab Legion had deployed in the area of the former British Mandate that was allotted to the Arab state, not entering the corpus separatum but massively garrisoning Latrun to blockade West Jerusalem once again.

Israeli victories against the Arab militias in the city pushed Abdullah I of Jordan to order the Arab Legion to intervene. Jordanian forces deployed in East Jerusalem, fought the Israelis and took the Jewish Quarter of the Old City, following which the population was expelled and fighters taken as prisoners of war to Jordan.