Umm,
short answer is that depleted uranium makes good munitions because its really dense and holds onto its mass on impact.
Not good for knives because contains no iron or carbon so cannot be hardened. Not sure how hard Uranium 238 is, Im guessing not too hard.
Too heavy, too toxic, particles from sharpening would kill you. Hours of fondling your custom Uranium knife would leave you cancer ridden and sterile.
If the military weren't using DU for munitions it would have to be treated as nuclear waste....Thats what it is.
Might make a good cartoon though.