Preface
While I believe some criticism of the chat reporting system is founded, I've seen a fair amount of lies and straight spread about the chat reporting system. In this thread I seek to disprove some of these false claims and leave my personal opinion at the end. Bold are statements of fact and other text is just additional information.
Forgery
Cheaters or the server are unable to forge signed messages as you, without having access to your computer's filesystem.
Context forgery no longer works (e.x. nodusclient/gaslight, video here); as the signature you send chat messages with is now based on the previous chat message. As such, if the real chat message signature is not based on the previous reported chat message (which in context forgery attacks would be malicious), your report will be thrown out and deemed as false. Here's a nice video with a visual explanation explaining why context forgery doesn't work anymore.
Report Endpoint Spamming
This endpoint will be heavily limited.
False Positives/Negatives
This issue exists with every moderation system, and isn't unique to Minecraft
Breaking the premise of Anarchy servers
Mojang are only going to be banning the worst of the worst and you shouldn't be saying racial slurs anyways, additionally Anarchy servers will most likely disable chat signatures with a plugin or jarmod.
Mojang/Microsoft will spy on your chat messages
The server has not been updated to send every chat message directly to Mojang, the only messages that are sent to Mojang are those the player reports to them.
My Opinions
While I'm not sure this was entirely needed or even asked for, I can see why Mojang and servers without enough manpower to moderate chat messages would want to implement this. This definitely won't impact the gameplay for me.
Mojang have also repeatedly shown they're not going to back down just because a bunch of teenagers with nothing else to do join a Discord server and start screaming "oh noes this is the end of minecraft!!!" and spreading misinformation