I have to agree. If your alternative is to have every other member ignore this user, why are you preserving their account? “Ghosting” is rude in real life, enforced this way on a forum it’s essentially bullying. Imagine standing in a room talking to people and no one’s even looking at you because you’ve been placed in an invisible box you can’t see.
Educate them on how to interact, use the features available in Discourse to enforce it, and then when they’ve continued to ignore your requests, invite them to move along.
Silencing temporarily can be a very, very effective tool.