I don't know that I agree. We don't know that this person is willfully ignorant. There are a lot of misconceptions about almost all religions. I think there is benefit in giving a valid attempt to set the record straight. After that, if they still refuse to understand or listen, then yes, it's best to just let them be in their ignorance.
This is my understanding, as a Christian, someone please correct me if I am wrong. I don't believe it is the
worship of Satan (or who we believe to be Satan) himself, but more likely a following of the
essence of Satan. Incorporating the ideas, attitudes and characteristics of Satan into daily life and world-views. "
You need to do what you want to do because life is short and then you're going to die so live while you can but take no crap from anyone" - to me, is an example of that. It is focused on 'self' and doing what makes the individual feel good. LaVey states about celebrating holidays "
The most important holiday in Satanism is one's own birthday, as the birth date of one's own god. To a Satanist, you are the most important being in the universe, and celebrating your own birthday honors your own vital existence." After self is one's family and then community (for some).
It helped me understand, perhaps it will help your friend as well.