The small bit of Through the Ages we got was free.
The entirety of A New Reign was free.
Winona was free.
They give away several skin drops for free a week, and recently they upped the amount of those that drop per week.
They gave the game itself free to anyone who already had Don't Starve when DST was in early access.
If you weren't there for some of those fine, but that doesn't mean they didn't happen.
They've given us plenty for free, a little paid DLC isn't going to kill you.