Why won't Unity games start on macOS sierra?

I have a fresh install of macOS sierra. I own several games based on Unity, all through Steam. The majority of them will not start. There is no error message. Steam tries to start them, but they close instantly.

It’s common to ask for a copy of ~/Library/Logs/Unity/Player.log, but the Unity directory does not exist.

The workaround for me was to go to the terminal and change the ownership of ~/Library/Logs:

sudo chown $USER ~/Library/Logs

(this requires the logged in user to have admin rights, and to enter their password)

Under macOS Sierra, ~/Library/Logs is owned by root and the logged in user cannot write to this directory. Changing the ownership is not an ideal solution - users should not have to learn unix to play their games.