I was going to post the same thing – I'm having this very issue on OSX 10.13, even though I tried opening the game on locations where I most definitely have write access (desktop, my home folder's Applications folder). I also tried expanding the downloaded .zip file via both OSX's default tool (Archive Utility) and The Unarchiver, just in case. Finally, I tried opening it from an exFAT formatted external disk, and in that case I got a different error – "Exception: Couldn't find file '._scripts.rpi'." (I can post the full stack trace if you want).
Regarding the "requires write access" error: clicking on "settings" -> "Main Menu" allows us to start a game, despite having this issue. However, when the game tries to create files outside of its container, an exception gets thrown. I managed to go quite far, but got to a point where an exception is thrown whatever I do, so I'm stuck.
Might this error have something to do with System Integrity Protection? You can't modify anything in /System, /bin, /sbin, or /usrbecause of that feature.
If there's any extra info you'd like to have to help fix this just let me know, I'd be happy to help.