It might be good that Facebook coins will attract more lay people to enter the crypto space because they will carry out extraordinary promotions where they are known for their social media so they also benefit from many loyal users, for the rest maybe new investors will read more many situations and will see high-quality coins like Bitcoin that continue to fluctuate every day, I believe there is a good side of Facebook to issue global coins.
If a large company starts coming towards the cryptocurrency then that's where we have to be quite vigilant, because it can be a two-edged sword. The bad impact that can come is also quite dangerous especially for those who have small projects but are quite successful in growing their coins. Global issues also can't just be solved by crypto.
You're right that global issues can't be solved by just this kind of system. Although, this is very much helpful but we know government doesn't want that crypto system would run the world. Maybe, it helps the economy at a certain level but solving the world's problem could seems difficult to figure. On the other hand, social networking sites really help spreading the information about cryptocurrencies and this gives impact which investors tends to get the attention on it.