l.google.com has some kind of DNSSEC error [1] but it seems to be required to load youtube.com
Google doesn't use DNSSEC, unfortunately, so this shouldn't be a problem. If your resolver breaks on this, I think that may be the result of a bug or misconfiguration, because there's no DNSSEC to validate here.
The argument that absolutely nothing that the world relies on, is not being singed (google Facebook reddit Cisco MicroSoft etc) holds no clout with the believers, unfortunately.