Initially, users were allowed to upload Pornography. However there have been several developments since that have lead to the current standing of Pornography being completely banned.
The main reasons for this is that the users who were uploading this content where no abiding by the rules, and the site became infested with pornography in all categories, without the 18+ rating. This made the videos available to children; searchable and on the front page of the site.
The drastic choice was made to ban it altogether as a solution to the issue.
There are still Pornographic videos in the system, and they are being removed as quickly as possible. It is likely that it will never be allowed on the platform again.
If you are caught uploading pornographic or graphically violent material, your account will be blocked, your content removed and you will be banned immediately. Your account and all of it's associated content will be forfeit.