Sorry to jump back a few comments, but:
...which helps no-one. If you put up a video and the video doesn't have captions then deaf people aren't going to be able to get the information out of the audio stream. It is therefore by definition inaccessible to them. To be accessible you must provide the information contained within the audio stream as an alternative format.
Forget about badges and levels, that's just common sense. And by removing sound you're making it inaccessible for blind users as well.
Actually, on a separate tack your audio stream should mirror the information contained within the video stream to be accessible to blind users. For example image a graph displayed in a video with no audio description; with no description of the information contained in the graph in the audio stream the blind user will not have access to that information.