There is, however, an ethical way to use other people's YouTube videos to create your own - by splicing and stitching several of them together, and YouTube itself gives you the tools to do it: Video Manager and the search filter.
In doing so, you're creating your own medley to cover the given topic in the unique way - this is YOUR contribution.
Here's how to do it:
- Go to YouTube and search for the topic you want to cover
- IMPORTANT: use the Filter to select Creative Commons License
- Select the best videos and add them to your list
- Use Video Manager to combine the videos together, chopping off the parts that you do not need
- [Optional] Record your own video intro
- IMPORTANT: give credit to the authors of the videos you've used, and
- Publish the video.
The good thing is that right now there are over 4 million videos on YouTube under the Creative Commons License - plenty to choose from to cover any topic you want.