Of course, individuals may find white noise personally irritating or distracting, and continuous loud noise of any sort is bad. But for others, noise can also help with relaxation, concentration, and sound masking. (I personally find white noise irritating, but I like brown noise.)
Also, this is not proven. I suspect the parent is thinking about https://www.theguardian.com/lifeandstyle/2020/oct/18/white-n..., which cites https://www.sciencedirect.com/science/article/abs/pii/S10870..., which found 1 study out of 38 which "suggested the noise may lead to more disrupted sleep" and concludes that more research is needed.
Of course, individuals may find white noise personally irritating or distracting, and continuous loud noise of any sort is bad. But for others, noise can also help with relaxation, concentration, and sound masking. (I personally find white noise irritating, but I like brown noise.)