I would personally see it as category 2 bug. There is currently a discussion going on at OSM and one thing brought up is: Its not possible to login or register with JavaScript disabled. It is possible to read without JavaScript, but its not possible. For some people thats a problem for various reasons.
On the other hand: i found this Disable JavaScript content. Possible? thread and it does not seem like this will be adressed for the reason mentioned there (Its a JS-App so use JS or don’t use Discourse)?
This isn’t a bug; it’s by design. Discourse is a JavaScript-based application running on Ember.js, so it would be impossible to turn off JS and still use the site. The way to accomplish what you’re wanting is to create a feature-complete static HTML UI, which is not on our roadmap, I’m afraid.