Let’s assume that stablecoin usage grows massively. Everyone everywhere has easy access. 

People in countries where the currency is less trusted will move lots of money to stables. 

What happens when these less trusted countries lose control over their local currency?

If it happens relatively quickly, those fiat currencies would inflate, the issuer would crumble.

Inadvertently , more of the asset backing the stable would be required, strengthening (deflationary) that asset.

The masses always win.

De-Fi or death.