By writing threat, I didn't mean issues like tether's issue. I mean, they are not coins, they are just usd and eur.
If you realize that point, then the question is moot. Bitcoin derives a lot of its popularity from the fact that its value is subject to the free market, meaning that its price moves according to supply and demand. Stable coins don't do that, and there is never going to be significant interest in them other than using them as a substitute for cash on exchanges.
So no, there isn't a stable coin in existence or one to be yet created that will present a threat to bitcoin, or to any altcoins.
What if we use bitcoin without these backup stable coins? We may need to learn that we can do without these stable coins, we don't need usd or eur or other traditional money. We should start using directly bitcoin rather than its usd value. For example, an apple may cost some satoshi not cents. Apple's cost depends the traditional way, demand and supply and its price can change in return for satoshis. We should remove usd eur and others, stable or not.