There's nothing wrong in buying a cryptocurrency that only focus for payments lol. It's like talking to somebody not to buy a safe haven token or a stable token like tether. It's for payment in their platform. I think it will be done for the marketplace on fb since there's a feature on that platform for marketplace. Plus buying stars for streamers.

Just make sure not to click ads on facebook or in other platforms that could mislead you in buying fake libra.