[Trotter]

Originally Posted by YouTube Terms of Service

5. Your Use of Content on the Site

A. The content on the YouTube Website, except all User Submissions (as defined below), including without limitation, the text, software, scripts, graphics, photos, sounds, music, videos, interactive features and the like ("Content") and the trademarks, service marks and logos contained therein ("Marks"), are owned by or licensed to YouTube, subject to copyright and other intellectual property rights under the law. Content on the Website is provided to you AS IS for your information and personal use only and may not be downloaded, copied, reproduced, distributed, transmitted, broadcast, displayed, sold, licensed, or otherwise exploited for any other purposes whatsoever without the prior written consent of the respective owners. YouTube reserves all rights not expressly granted in and to the Website and the Content.

B. You may access User Submissions for your information and personal use solely as intended through the provided functionality of the YouTube Website. You shall not copy or download any User Submission unless you see a “download” or similar link displayed by YouTube on the YouTube Website for that User Submission.

D. You may access YouTube Content, User Submissions and other content only as permitted under this Agreement. YouTube reserves all rights not expressly granted in and to the YouTube Content and the YouTube Website.

E. You agree to not engage in the use, copying, or distribution of any of the Content other than expressly permitted herein, including any use, copying, or distribution of User Submissions of third parties obtained through the Website for any commercial purposes.

Source

Downloaders violate the Terms of Service laid out by YouTube.