Read the url I posted. Example after example of dogs injured by torn dew claws, posted by people who saw the injury first-hand.

My dogs do obedience, some at CDX level, and field and the youngest that had the dew claws removed lived to be over 14 with no unsoundness in front. If agility dogs are having problems, I would guess that jumping them on hard surfaces has a lot more to do with it than presence or absence of dew claws. I train outdoors on grass.

I can't figure out how coyotes, wolves, and foxes survive without humans to remove the dewclaws from their whelps if it is such an issue in the field. IMO, breed for nice tight feet, including dews held close to the leg.