As @anon41602260 noted you can disable fonts you don’t want in Font Book. FB shouldn’t allow you do harm by disabling fonts from view. I wouldn’t delete anything though.
Some of the fonts in /System/Library/Fonts, known generally as the “system fonts,” are essential to the operating system because it uses them for menus, dialogs, and other system-level things; deleting one of the essentials can render your Mac so helpless that it won’t even start up, and you’d need administrator access to add fonts to or delete them from this location. Be careful if you try this.
There are likely fonts installed in macOS you don’t and won’t use, but I generally find it’s better safe than sorry to let be fonts installed by the system.