Look at the Robin Williams situation. He specifically banned using his likeness for 25 years after his death. That was a clear, stated wish. But most artists don't leave those kinds of legal documents. So we're left guessing. Thats the problem.
Your argument assumes AI can somehow channel an artist's intent. But intent isn't data points. Its a living, changing thing. Van Gogh painted over his own works when he changed his mind. He'd scrap entire compositions. If he died mid-painting, and AI finished it based on what was visible, it'd be finishing a version he already rejected.
Without explicit permission from the artist themselves, we're just projecting our own desires onto their corpse. That's not respect. That's grave robbing with good marketing.