Youtube’s Terms of Service
When you use the site you are agreeing to abide by its terms. This is a contractual relationship between you the user and YouTube. YouTube’s Terms of Service state:
“Content is provided to you AS IS. You may access Content for your information and personal use solely as intended through the provided functionality of the Service and as permitted under these. You shall not download any Content unless you see a “download” or similar link displayed by YouTube on the Service for that Content. You shall not copy, reproduce, distribute, transmit, broadcast, display, sell, license, or otherwise exploit any Content for any other purposes without the prior written consent of YouTube or the respective licensors of the Content. YouTube and its licensors reserve all rights not expressly granted in and to the Service and the Content.”
In other words, unless there is a download link for the video, downloading it using a YouTube downloader tool would violate the YouTube Terms of Service contract you agree to by using the site. The existence of intellectual rights on the videos is another, independent consideration.
Important clarification: TechSpot is strictly committed to legality and will not entertain illegal content or assist in any illegal actions. Now, I'm not preaching or telling anybody he shouldn't download YouTube videos, and I'm not even saying I haven't done this myself. I am merely informing on the legal aspect of the activity and on TechSpot’s general policy regarding legality of posted material and advice.