They just installed Windows on their netbooks last time it was even cheaper. The people who think steam deck will make linux mainstream are going to just see the next deck come with windows and everyone who gets a deck installing windows on it to play games.

They might, but they'll be getting Linux for the wrong reasons. And will end up dissatisfied because they'll be expecting Windows only free. Which will hurt adoption more.

FLOSS was never about free as in beer.