Artists use pure black all the time. "Never use black" is something said to beginners because never using it is better than using it excessively. It's like saying "never use passive voice" to a beginning writer. Black is appealing if used correctly, and because all commonly used printing and display technologies have lower dynamic range than typical real-life scenes, careful use of pure black and pure white is essential if you want an appearance of realism.

And typography is a completely different subject to painting. People have aimed for darker blacks from the very beginning of ink technology. Even now, people put up with the hassle of dip pens instead of fountain pens because they allow for darker black inks. Extremely high contrast is considered a mark of quality in printing, so why should it be any different on screen?