I have enjoyed several of the
Hitler Learn type of videos. Some are very well done and extremely creative, however, they do violate the copyright of the original movie production and are soon forced to be removed from the Internet.
There are a few that will likely never be seen again.
However, if you want to preserve a copy of your favorites, visit this site and you can get a copy made that resides on your PC. For free yet.
http://keepvid.com/Just don't use your copy for commercial purposes and you are legal, and, in my opinion, moral.