You’re focusing on all of the negative possibilities, rather than the positive uses. If you’re claiming that the ability to edit messages will take away from freedom of speech, then explain how that is any different from simply purging the messages of the people in question? None of the examples I have used even come close to infringing on freedom of speech. Technically, there isn’t freedom of speech anyway, since, most channels have rules regarding proper conduct in chat.
As for positive uses, take for example the translation bot. If only the ability to edit messages was added, you could check a message when it is sent to see if it can be translated, then edit the message to contain the original message as well as a translation. When I was moderating for 14k people at one time, we had many, many, foreign users in chat. So rather than time them all out, which would be alienating an entire group of people, I made a bot that allowed me to see their translated messages to decide if their content was appropriate for chat. However, if the ability to see messages before they are sent was added, you could see the foreign message before it is sent, then translate it en-route so it is posted as a translated message.
There are no queue-like properties to the pre-screening, essentially what it would do is send the message to a function to get a return value, if the value is returned as false then the message is not sent. If the return value is a string, it sends that message instead, and if there is no return value, it simply sends as written. It’s not as if there are a list of messages waiting to be checked.
In the future I implore you to think more positively about potential features instead of shooting them down due to the possible negative uses of them. If every useful thing that could be abused was discarded, there would never be any progress. Everything can be used for good, or evil, but it all depends on who’s implementing it and in what ways.