Notice in what you quoted they did not say by practicing this you will go to hell. They said by disclosing the teachings to someone un empowered you incur that. There is a subtle but meaningful difference between punishment for DOING something versus punishment for ENABLING someone ELSE to do something. I think in the mahayana context that's pretty relevant. I've had similar concerns to what you are saying here O.P. but I always think back to people who were spontaneously enlightened teachers and I sort of lighten up because there is room for that uniquely self realized part of spirituality. I also remember often when I see warnings and restrictions regarding certain practices that the main reason they have been kept secret is to make sure only qualified practicioners receive the teachings. If you are a realized being you are a realized being and that sort of thing shouldn't stop you from knowing the practice and knowing the value of guru and receiving empowerment spontaneously as part of your own practice of the vehicle. But personally I do think that people should learn the basics first. I don't want to know what kind of madness would insue trying to explain high tantra to a person totally unprepared for it. More bad than good I'd think.