Soft down wouldn't be a problem, but my upper-lip hair is so dark and dense it's a visible 'tash from across the room (NOT my imagination - it's visible on photographs). I bleach it when I can, but I can't do it very often as the bleach makes my skin sore, nor can I leave it on long enough to totally remove the colour. The hair on my chin is, for the most part, quite light coloured (except the odd very dark one, which I pluck), but in certain areas it's very long (over half an inch) - not a good look!
There is no scientific reasoning behind any form of hair removal encouraging growth - hair removal methods that cut the hair make the re-growth look denser as the tip of the hair is blunt and the shaft thick, rather than a hair that has re-grown from the follicle which is tapered to a fine tip.