I would like to play devil's advocate From this article I read
Quote
Unlike the volatility seen around other cryptocurrencys in the past, we believe that Libras focus on creating a stable, low inflation currency backed by a reserve or real assets is a differentiator. Further, unlike other stablecoins, Libra will not be pegged to one currency but instead a basket of assets ranging from bank deposits to short-term government securities.
And if ever it is launched, it will definitely bring down Bitcoin's dominance percentage in the market because it will eat some percentage on that 100% pie. The extent on how huge is still unknown because it has yet operating. Yes, it is a very controversial currency but I believe it won't eat much of Bitcoin dominance since not all facebook users will be using Libra automatically.