Some artists didactically insist black should not be used in a painting, often supported by the argument that the Impressionists didn’t. Do you ever hear it said about any other colour?
If you wouldn’t use black to darken a colour, then perhaps using white to lighten it shouldn’t be automatic either? The main problem is few colours are light in tone (though some do come in “light” and “dark” versions). You might lighten a red with a bit of yellow, but how would you lighten a yellow?
I think where “don’t use white” should be considered is when you’re working with the lightest tones on a painting. Don’t automatically use pure white, use very pale yellow, blue, red, green, purple first. Take a look at Monet’s snow paintings to see what interesting colours “white snow” can be (for example Lavacourt under Snow in the National Gallery in London).
A monoprint I made a few years ago has pale blue that seems lighter than the white of the paper (the top one in the photo). I think it’s the coolness of the blue that does this, against the warm white of the paper.