I’ve read this thread,
Dropdown menus by CSS or JavaScript
but see that there are conflicting opinions over use of CSS only vs javascript for dropdowns.
Is the only argument in favor of using CSS only to accommodate people with javascript turned off?
Are there any other considerations?
Which method is more forgiving in a site that must work on desktop and most mobile browsers (iOS, android)?
Drop down menus tend to be designed for pointing devices. It is very rare to find one that can handle linear (e.g. keyboard tabbing through items) or touch interaction (although you can degrade gracefully if the top level items link to pages that provide onwards navigation).
I doubt it is possible to get one that works well for linear or touch without JavaScript.