A stablecoin-margined position is described as safer than a coin-margined one because the collateral does not move with the asset. That is true of ordinary market risk and it is not the whole risk.
The collateral is a token whose value depends on an issuer honouring redemption. Usually that holds. When it does not, the token trades below a dollar — a depeg — and everything denominated in it reprices.
Why it hits everything at once
A depeg is not a position-level problem. Margin across the venue is computed in the stablecoin, so a discount to par reduces every account’s equity simultaneously.
That is a correlated shock of the worst kind: it arrives at every leveraged position on the venue in the same instant, in the same direction. The result is exactly the mechanism in liquidation cascades, triggered by the collateral rather than by the asset.
The reflexive part
Holders of a suspect stablecoin try to exit into other assets, which can push those assets up in that stablecoin’s terms — so prices quoted against it become unreliable at exactly the moment you need them.
Any figure quoted in that unit is now ambiguous: has the asset risen, or has the unit fallen? A mark price built from an index of venues quoting in the same stablecoin inherits the problem rather than solving it.
The practical questions
Which stablecoin is your margin actually in, and who issues it. Whether the venue accepts more than one as collateral, and at what haircut. And whether your quote asset and your collateral are the same token, which concentrates the exposure rather than spreading it.
A chain that quotes and settles in a stablecoin issued by the chain’s own operator concentrates it further — the structure noted in Robinhood Chain.
The framing
This belongs with venue risk rather than with market risk. It is not hedgeable with a stop and it is not solved by sizing. It is a question of what you are holding and who you are relying on, and the honest answer is to know rather than to assume.