I've added another taboo topic among racist western progressives around the Arab-Jewish conflict in the Middle East: demographics.
One cannot talk about the demographics of the land of Israel as it was under the Ottomans. The reason that you cannot talk about that is because it may call into question just how many Arabs were living there prior to the Mandate and this will tend to undercut Arab claims to the region, particularly given the fact that the Jews were a majority in Jerusalem.
The fact of the matter is that a large percentage of the local Arabs came from neighboring countries and regions. Some percentage, probably a small percentage, had been living there for a long time, centuries even, but the fact is that many, many "Palestinians" are people whose ancestors were from Egypt or what is now Jordan or Syria or Iraq and elsewhere.
This fact is entirely taboo among racist progressives who hold that the "Palestinians" were there as a discreet people since before the birth of the Sun.