I don’t think people are saying Israel shouldn’t defend themselves, it’s more about why the strikes are happening in the first place. It’s like if Russia built a giant defense system to keep out Ukrainian missiles. The problem isn’t that they’re defending themselves it’s what they’re doing to provoke it.
As for why the attacks are happening, like you said it s a very complicated issue. But in essence Israel has kicked a bunch of Palestinians out of their homes and illegally annexed their land, in violation of international law. They’ve also continued to violate the human rights of the Palestinians that remain.
If you want to read more: UN: https://news.un.org/en/story/2022/10/1129722 Amnesty International: https://www.amnesty.org/en/latest/campaigns/2022/02/israels-...