http://j4dhkkxfcsvzvh3p5djkmuehhgd6t6l7wmzih6b4ss744hegwkiae7ad.onion/en/blog/disnews-11
This essentially would allow government (or anyone else for that matter) who's in possession of such certificates to intercept encrypted data you exchange with the website and view it in plain in real time. For example, emails you send, posts, you upload, images you view, things you download or upload, people you communicate with.