I understand that you fight for your right to denounce war crimes and genocide.
However, please also consider that the location of the server influences the mod teams.
Mas.to is located in Germany; a country where chanting "From the river to the sea" is prohibited https://www.ynetnews.com/article/hkhznye50 (ynet is not an exactly neutral source, but the sentence is correctly represented).
And this is not even taking into account that in Germany the discourse is on a very different level. Public opinion has already shifted and people are mostly against the genocide (with some noteworthy exceptions like most politicians and a surprisingly large part of people who consider themselves as 'leftists'), but for many, it is still a challenge to let go the idea that zionism is a necessary project to protect Jews.
'Child murderer' happens also to be considered one of the fundamental historic antisemitic tropes. https://en.wikipedia.org/wiki/Blood_libel
Ironically, the joke is on Netanyahu and modern far right zionism, considering the infant deaths in Gaza (and likely your post was referring to these proven crimes). But maybe this background perspective helps you to understand why 'child merderer' is a taboo to say in the context of Israel. (We don't have to argue here about the far right Zionism's strategical conflation of "Israel=Jews" and why this is a very bad idea, but it is a fact that this discourse shapes discourse and policy, especially in Germany).
I don't know the mas.to mods, but it is likely that some of them have ties to Germany, and they are scared about the potential backlash when allowing such content.
Thus: talk with them, discuss the issue (as I said, discourse in Germany is also shifting), but be also aware that some stuff that might be acceptable in your circles, can't be said in Germany, for social and legal reasons.
Do the exercise and put yourself in their position (assuming they're not hardcore Zionists but people worried about the potential social and legal consequences for their moderation decisions). Also, even if they agree with you on the condemnation of Israel's crimes, it might be that they consider this specific post as counter-productive achieving the goal of stopping the genocide, because the use of messages that align with antisemitic tropes is a) dangerous and wrong, and b) makes the Israel supporters (who bear a huge responsibility in facilitating this genocide) rally harder around Netanyahu.
Does it suck that you feel censored/tone-policed because these mods from another place have sentiments that seem absurd to you? Probably.
But still, trying to understand the other side maybe helps you to get some perspective.