Discourse depends on PostgreSQL running in a shared volume; and a lot of other important files are in that shared volume (images, uploaded files, backups, logs, and more).
If you maintain the file system integrity of the /shared volume, according to Discourse configuration standards, then you can start and stop a Discourse Docker image and container application with ease; however, you cannot build the application (to my knowledge) without the Discourse scripts (unless you do a full reverse engineering on the scripts and write you own script based on the perfectly good working and supported scripts) because the scripts are responsible for building a sophisticated EmberJS SPA (client side technology) on top of Ruby on Rails (a server side technology), not to mention managing the configuration of the core application and all plugins. It’s quite a sophisticated application, to be honest.
Yes, you can start a Discourse container or create a Discourse container from a Discourse image without any scripts, if (and only if) you already have built a perfectly good Discourse Docker image which complies with Discourse configuration standards, including the persistent storage requirements for the database, images and uploads, backups, log files, etc. There is a lot of important files required for Discourse in the shared volume; and so you cannot just “take a plain vanilla Discourse Docker image” and spin it up and running without all the required prerequisites mentioned above (and not all was mentioned above!)
Hope this helps.