"Disproportionate force" means that many people and countries resent the fact that Israel has a military advantage and thus create new rules where the militarily superior power must respond with "proportionate force" when attacked. Of course, this standard only applies when Israel is the militarily superior power. I don't recall anyone requiring Sri Lanka to use proportionate force when fighting the Tamil Tigers or the US when fighting in Afghanistan or the Lebanese army when fighting in Islamic extremists.
U.S., allies conduct 1 air strike in Syria and 11 in Iraq against ISIS militants (Reuters)
from the article: UN rights body ready to debate Goldstone probe