A purist will tell you that unless you start and finish a painting outdoors, then you can’t call it a Plein Air painting. A purist will tell you that oil paints are the only true medium. A purist will tell you that using anything but lightfast pigments makes your work less legitimate; even worse, that digital painting isn’t ‘real painting’.
The thing with pure is that pure always changes. Right now, the purists turn their nose up at acrylic artists because ‘it’s not the real thing.’ Back in Turner’s day, you never had the real thing unless your assistant spent hours on end grinding your pigments on location for you. Does that mean that oil painters who use tube-paints today are any less pure or legitimate?
Art and technology co-exist. It will continue to do so forever. That doesn’t make an artist’s work today any less ‘pure’ than yesterday’s artist, or any purer than tomorrow’s. What matters is that artist’s are making work they want to make. Work that matters to them. The medium is, in so many ways, impure, no matter when and how you look at it.