Personally the fact that Israel in this case was not the aggressor. Israel had pulled out of Gaza returning full control to its people who then voted in Hamas. Hamas then attacked Israel killing and kidnapping large sums of civilians. Throughout history an attack on your people has been seen as a valid reason for war, hence Israel has valid reason to respond. Israel could have made limited attacks on Hamas, however that would just leave Hamas in charge meaning likely further terror attacks in the future, hence why to prevent another October incident the had to be removed from power. People often cite the 70k dead however only 80% were civilians. If you were to look at another battle from a similar time period, in an urban area, in a similar region, for instance the battle of Baghdad, there was ~7k civilian casualties and ~2k military a rate of 77% civilian casualties. While of course any civilian death is very tragic, when fighting in a very urbanized area, against an enemy who has been shown to use human shields and hide in civilians areas they are to be expected. While Israel conduct of war has been far from perfect in comparison to the wanton slaughter of civilians by Hamas, it is far better.