Please do downvote ALL pirated and copyright infringed videos. The problem though is that not all copyright infringements are easy to spot, and sometimes it can be a legitimate owner of a Youtube channel reposting their content on Dtube, and you should not penalize them because you did not realize it was their own original content.

I guess all legitimate youtubers should make their account names match their youtube channel names, and mention in their video description that it is in fact their own original content.