I'm with Caro on that one.
I find loads of Border Collies in agility, loads of people around here got one because they think they should have one to be a serious nationals/world class competitor... You can easily see the difference between the ones who got a Border Collie for the right reason and ones who didn't. I enjoy the Border Collies who got the right home, the right and careful socialization, exposure, exercise and positive training usually founded on obedience first and agility second.
... Then the other ones are fear biters, very dog reactive, need loads of personal space, crazy drive but no outlet, get carried off the course for self rewarding doing their own course and don't have much of a recall to speak of because they have been tricked and BC's are smarter than most dogs and pattern so easy it makes your head spin, lol.
Wayyyyy too many dog reactive and aggressive, obsessive compulsive disorder ones being bred as well.. together with less experienced handlers make a bad combination, imo.
Obviously the latter can happen with any breed if you don't be careful, etc, but the propensity to potentially messing them up is too high lol
Of course this is just anecdotal and my personal observations over the last three years. Shelties love Shelties, I found most Border Collies are too intense for my Shelties' liking, they don't play even with the really nice ones, lol