Public chats are, well public. If you are in a public chat then everyone can see what you say. Encryption or any other attempt to make it private are silly here. If you are in a private, encrypted group, then only those people can see what you say (unless someone leaks). If you are in a e2ee personal chat with one other person, then only the 2 of you know what is being said. If you send a regular email that is the same as a postcard and anyone can look at what it says. You choose where and how you want to speak and adjust accordingly.