Can't disable fonts in Font Book after fresh Mojave install
It turns out that (as far as I know), Font Book in Mojave just does not allow disabling of the default fonts.

There are two main locations where fonts are stored under Mojave:

/Library/Fonts/


/Library/Fonts/ contains all the general use fonts, available to all users. These are the fonts I wanted to disable.

/System/Library/Fonts/


/System/Library/Fonts/ contains fonts that are necessary for the system.

I simply moved all the fonts from /Library/Fonts/ to /Library/Fonts (disabled)/

It went fine and the system has not complained so far.

I did leave copies of the standard web fonts: Verdana, Times New Roman etc.