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.
I don't think there's any threat to bitcoin as of now. Bitcoin still prevails as the most used and trusted by many cryptocurrency users. Stablecoins are controlled and somewhat centralized, it is condtradicting the essence of crypto being decentralized.
Stablecoins is much preferred when using as payment because price fluctuations are minimal. However for day traders, bitcoin still would be widely used sincetraders want price action to gain profit.