In a premium product like a MacBook, I'd expect Apple to replace any fault like this no questions asked. And if it happens again, replace it again. And if it happens again, offer a full refund.

It doesn't really matter if these cracks are caused by issues in apples glass-making process or caused by users shutting them on bits of rice. In either case, the machine isn't suitable for its usecase. And on a premium product, I would expect the manufacturer to make it right.