This is as good an explanation as you’re likely to find….

“Israel claims that it is ‘defending itself’ that it is not attacking civilians, only ‘terrorists’, while we claim that Israeli is indeed involved in a very conscious campaign of ethnic cleansing of Arab lands. But because the average person does not believe that psychopathy among our leaders exists, that our leaders are just like you and me – fundamentally decent human beings – the public looks at these two opposing arguments and concludes that the truth must lie somewhere in the Middle. Yet such an analysis does not take into account that one side could be 100% lying and the other 100% telling the truth. As a result of this human tendency to conclude that the truth lies in the middle, the liar always comes out on top! His lies are given credence to some extent while the truth is watered down! In the case of Lebanon and Palestine, Israel is lying, Israel is consciously murdering civilians, that is the truth, yet because no one can believe that there are people who would actually do such things, they believe that the truth is exaggeration or ‘conspiracy theory’.” – Alternative News

Yup.