Isn't the whole point of hostages or human shields is that you're supposed to not kill them? I think it's generally seen as bad if you kill civilians when taking out "bad guys".
I do not understand why this became such a huge argument for why the Palestinian casualties are so high.
It is also meant to be passing the buck on to Palestinians at large. If you aren't actively fighting against Hamas you're part of Hamas and thus a legitimate target.
This is of course propaganda aimed at making Israeli people more on board with killing Palestinians. Their western allies repeating it to make their citizens more on board with supporting Israel is a side effect.