As I said upthread, under international law, even if militants hide in populated areas, it is still illegal for states to bomb those areas and kill civilians.
It's usually considered disproportionate, as seen in this case, where to kill one militant they killed nine civilians, including children.
Earlier Israel also bombed a building that they knew housed media (by that I mean they admitted publicly they knew reporters were there). The apparent intent was to take out Hamas communication equipment on the roof. They blame Hamas for putting it there but clearly it's illegal to put civilians in harm's way to take out communications equipment.
When judging whether something is disproportionate, you are looking at very limited factors. You are not basing it on the wide sweep of history, who started the conflict, who's been most reluctant to negotiate, etc. It is really based on the military factors at play. I don't really see how you can argue that what Israel is doing is proportionate, or that they're showing enough discrimination. They're conducting airstrikes in one of the most heavily densely populated areas in the world.
I got this off twitter earlier and I fully agree:
"#Gaza is just 40km long &10km wide & home to nearly 2M people. It's not the best place to fight a war if you want to avoid killing civilians "