Interesting point, however you have to understand the Palestinian people have been suffering from Israeli oppression for decades and its of no surprise to me that they voted in Hamas. We had a couple of Palestinian students visit my uni a couple of weeks ago. Some of stories they had were awful. The IDF well and truly treats them as third class citizens.
Because its Israel. Something in me tells me that had Hamas carried out a similar atrocity, it would have been pasted on every news paper across the globe, and even now it would still be front page news. Israel can break every law, UN resolution, and Geneva convention and neither the US or the UK will do anything about it.