If you understand how Bitcoin works, then no, Stablecoins are not undermining Bitcoin's original mission.

Stablecoins are most not decentralized by Bitcoin is. Stablecoins can be "frozen" in people's addresses, Bitcoin can not be frozen. Stablecoin can be minted out of a thin air and mostly use POS, Bitcoin uses POW to generated new coins into the network

Those who understand the main purpose of Bitcoin won't see stablecoins as a threat