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.
They are a bit misquoting. Which is understandable, as there is a ton of propaganda out there. There is a ton of uncertainty, too.
The UN report also wasn't about proofing the negative of Hamas using human shields ever, but it was about a specific time frame and specific legal definition of human shields and specific cases.
The red crescent for example (you can - especially if you read Arabic - find reports and videos of a member of them who was working as medic in a Gaza strip refuge hospital) has called out Hamas as using the hospital area as place to launch rockets from, which was answered by shelling of them after one dud air strike and then deadly ones (which is practice sometimes, but not always). You can imagine how hard (read impossible) it is for some people who are injured to evacuate in a timely manner.
There are also credible reports that Hamas regularly tortured and killed people in the strip (read:Palestinians) and used hospitals for the torture. You can find the reports of you search for Hamas take over of the Gaza strip. Doesn't mean the other patients are good targets for air strikes then.
I would like to underline that there is a false dichotomy of Israel - the Jews - the IDF on one hand and Palestinians - Palestine - the Diaspora - Hamas - Fatah - sometimes even 'the Arabs' on the other side, which is wrong.
While most of the mentioned groups are involved in the struggle for a safe state without some oppression - and especially only we ought to support fights against oppression - it is important to see how different the actors are and how many are involved. It is also important to see the connections between the individuals - nearly everyone is working class, or forced lumpen.
A socialist solution in the region demands a widening of the narrative above a fictive religious god given homeland and demands critical support - which has to be practical: read this as more than posting - to strengthen the alternatives to semi - religiously motivated forces within the current territory of Israel/Palestine.
There is a Jewish Israeli left, there is a Israeli Arab left (who often isn't as fly as you would guess from twitter in relation to Hamas), there is a Christian minority in the strip and some of them are left. There are also people who are either culturally (rare) or practically atheistic or the above labels don't fit and there are leftists, too.
Within Gaza (no clue how it is in Jerusalem/West Jordan) there is a ton of trauma and hurt, though the multiplicity of thoughts, groups and political action is high. Hamas is not equivalent to the Palestinian people (though got a majority of support a couple of years back, but that doesn't mean there aren't good reasons to see them ambivalent - do you remember what the Jerusalem conflicts started about or do you talk about rockets and arrow strikes only now? It was about the fundamental question of land).
As leftists we should also be aware that (when all of this is over) the uncritical support for some needs to be critical support and we have to look in the problems of Hamas (esp. the violence against leftists, LGBTQ comrades, etc.), but also problematize specific (instead of as a blanket) IDF attacks. The question of land, resources and class are fundamental as tools earlier, but the daily practices of 'securing' are what ought to be looked at - those are related to and build the material conditions of life in Egypt, Jordan, Syria, Lebanon, Palestine and Israel.