None of these are mutually exclusive statements. You can understand that Israel propped up Hamas to label their aggressive tactics as “terrorism” and use that against all Palestinians, while understanding that those “terrorist” tactics can indeed be effective.
The US propped up the Taliban and other right-wing terrorist groups in Afganistan in the 80s to oppose their then secular Socialist gov and the supporting USSR, and we all know how that came back to bite them later. Just because a country props a group up doesn’t mean it’ll always keep doing things beneficial to them.
are upset by how Israel is doing it too
“Terrorist” tactics (or anything really) used for the sake of driving out a settler colonial ethnostate (a good thing) - like Hamas are doing and Viet Cong did - is good, while those tactics when used to oppress and commit genocide on a native population (a bad thing) - like Israel is doing - is bad. This isn’t that hard to understand.