The terms of the contract are the terms encoded in the HTTP protocol. They are:

- I, as the user, (or my user agent on behalf of me) ask for a resource.

- YT, as the provider, (or the server on YT's behalf) decide whether to send that resource to me.

- If you do, I'll use or not use it in accordance with my user agent configuration.

I asked for the video, and YT chose to send it to me. I'm not going to lose sleep over the morality of using the web as it was intended to be used.