There's really no reason not to.
Quad9 already states that they strongly oppose piracy, so just block the sites. The piracy sites will be fine.
I don’t think DNS is as neutral as Quad9 believes it is. DNS is like the sign for a business on the road and the domain registrar is like the building permit you get to build the sign. DNS is a way to find a website or business without even bothering with a search engine. Try typing in stamps.com, office.com, booking.com, weather.com.