The censorship is intentional on the part of Facebook, but the "silent" part is a frontend bug on messenger.com (possibly also the app). Normally it shows you a red "error" indicator next to the message that says something like "this goes against our community guidelines.
The error can be seen in some of the screenshots. It briefly shows "couldn't send" and if you refresh the page the messages disappear forever.
There are replies to another comment about it being a bug. They are saying that's just a cover. Standard conspiracy stuff.
But people are also questioning the whole idea of blocking messages at all. Everyone thinks they don't need to be protected, but the fact of it is that we're all vulnerable to manipulation. Hell, that's one of the issues that people take with media platforms. Their content selection algorithms and targeted ads are manipulative.
The error can be seen in some of the screenshots. It briefly shows "couldn't send" and if you refresh the page the messages disappear forever.