This error is due to an abundance of caution in preventing the daemon RPC from being accessible from the outside without the user really understanding the consequences.
Here, if you really intend the RPC to be accessible from other machines, you can just add
--confirm-external-bind to your command line, as the message says. Adding this option serves as a confirmation from the user that they really underand that (unencrypted) external access will be enabled.
Alternatively, if you know how set up an SSH tunnel, you could do that instead, which would allow listening only on 127.0.0.1, while allowing tunneled access to the external machine you want to use it from, with the advantage of encryption and authentication (and I don't know how to do that offhand, but looking for ssh tunnel on duckduckgo should give good pointers).