The challenge is to the legitimacy of the methodology Israel uses, not the legitimacy of the state. The Mass destruction and insensitivity to civilian infrastructure and utter disregard for civilian collateral damage and death is what is called into question as legitimate. The blaming of all civilian collateral damage Israeli forces inflict on those damaged is also not legitimate. Until the IDF and Israeli politicians come to understand this, they will never see the difference. The late 19th century concept of punitive reparations and right of conquest that led from the first World War to the second was something the Brits and French didn't get either.
Iraqi car bomb death toll rises to 25 (Reuters)
from the article: MI Chief: Israel's success battling terror has turned world against us