There are multiple ways to avoid a detective catching you because of DNA (Flare gun, decoy) and hell sometimes you can use that in your advantage (lure a detective in the nether or a secluded spot on the map) so I wouldn't want the DNA being removed from knives.

There are multiple ways to avoid a detective catching you because of DNA (Flare gun, decoy) and hell sometimes you can use that in your advantage (lure a detective in the nether or a secluded spot on the map) so I wouldn't want the DNA being removed from knives.