Automating imessages has been an official thing in macos since ages that i know of, but it is done on a computer rather than a phone. The argument that opening up automation for imessage will increase spam does not hold, just because automation is already opened up, thus whatever spam this allows or not is already here.

EDIT: example script to run from a mac terminal:

    osascript -e 'tell application "Messages" to send "$message" to buddy "+12345678" of (1st service whose service type = iMessage)'