It doesn't just look bad when it's still, it's actively distracting while scrolling due it causing flickering. The only time dithering should be employed is to

It doesn't just look bad when it's still, it's actively distracting while scrolling due it causing flickering. The only time dithering should be employed is to get rid of nasty banding. Otherwise just serve lower resolution images or use tricks that aren't nearly as noticeable like compressing the chroma more than the luma.