Would you allow the same middle ground fallacy for Holocaust?
Check the dates.
If you were trying to assess claims of an extraordinary and unprecedented mechanised genocide by Nazi Germany in 1943 or early 1944, when it wasn't obvious what was actually going on, and when all people had to go on were reports from a handful of escapees and refugees, then yes, being careful with the evidence would be the appropriate response to the Holocaust claims available at the time, just as being careful with Cambodian refugee reports would have been appropriate in 1977 or 1978.
Quite contrary, it was fairly well reported. The reason Chomsky grudgingly accepted the fact of genocide was the Third Indochina War, when coincidentally in 1978 the communist Vietnam moved in to displace Pol Pot. Were it not Vietnamese but say Americans, he'd deny the genocide to the day.
Right now he denies that chemical attacks by Assad govt have happened in Syria, so the old man is still in the same denial business - OPCW reports be damned.
That sounds pretty balanced to me.