A very very great deal of anger is acceptable when it is in the service of universally uplifting humans rather than inflicting death and despair and degradation upon them. I suppose I am more mournful than angry, but anger is appropriate and widely accepted.

Very much less anger is acceptable when it is not distinguishable from, "In this complex conflict, my side gets to murder and torture until the conflict is resolved in my side's favor."

Israel claims to not have adopted that ghastly outlook, but when the rest of the world looks at its actions, its outlook in practice is not quite so clear.

But neither is yours, as expressed here. You take the central event that prompted the conflict and dismiss is as "whataboutism"! It's not whataboutism to address the act of egregious terror that prompted the events. That's the entire core of the issue.

It is reasonable, I think, as a humanitarian, to be quite angry at the Israeli government for prosecuting a war against Hamas while inflicting so many civilian casualties and causing such poor conditions for everyone surviving in Gaza. But it is not reasonable as a humanitarian to not simultaneously be apoplectic with fury at Hamas for striking to cause the maximum human carnage possible given their capabilities, and then doing their very best to make sure that any consequences they suffered in response would be felt tenfold by the population who is supposedly in their care.

Sadness can be expressed much more easily without needing any sort of balance. But anger assigns blame. Anger suggests a vehement counter-response, and implies who is right and who is wrong. If you want to be publicly angry, you have the responsibility as a humanitarian to appropriately direct that anger at all the responsible parties. Because to do otherwise is to condone atrocities. If for whatever reason you can't bring yourself to apportion anger to all those responsible, at least not right now, then being outwardly "nice" is the humanitarian alternative.