"The court held that merely clicking on a download button does not show consent with license terms, if those terms were not conspicuous and if it was not explicit to the consumer that clicking meant agreeing to the license."
I'm not a lawyer but I think even if you offset the legal responsibilities to the user by alerting them with copyrights prompt it's still illegal to download youtube videos.
United States v. Auernheimer, 748 F.3d 525 (3d Cir. 2014). Specifically, on page 12, footnote 5, the court states:
“We also note that in order to be guilty of accessing ‘without authorization, or in excess of authorization’ under New Jersey law, the Government needed to prove that Auernheimer or Spitler circumvented a code- or password-based barrier to access... The account slurper simply accessed the publicly facing portion of the login screen and scraped information that AT&T unintentionally published.”
https://en.m.wikipedia.org/wiki/Specht_v._Netscape_Communica...