Let's discuss the potential effects of stable coins which are bound to usd or eur. We usually use them to avoid the volatility or short bitcoin in a way. There are many stable coins in the last year. By writing threat, I didn't mean issues like tether's issue. I mean, they are not coins, they are just usd and eur.
To my mind, stable coins (e.g. Libra) won't be a threat for Bitcoin. Bitcoin will continue to develop and be among the top currencies in the future. Besides, stable coins can be used by governments after fiat money loses its worth.