I am not a fan of crossbreeding for anything, but it is worse when dogs are crossbred for companion purposes. If you can't find your perfect dog in a purebred, then go look at shelter dogs! There are so many different personalities out there, so it would be almost impossible to not find what you want in a companion. It irks me to no end to see neurotic doodles and micro-tiny-teacup-chi-schon-poo-morkie things that have terrible health and even worse personalities. I know that there are some "responsible" doodle breeders out there in the sense that they health test and whatnot, but to me breeding mixes like that is a form of irresponsible breeding.
As far as sport mixes go, I am not fond of them. I am looking at a sport-bred BC for my next dog, but a lot of the kennels I find also breed sport mixes like border-whippets, border-jacks, and border-staffys. These kennels produce litter after litter of dogs, and all of it is merely so that they can win in a sport. I just think it is a useless breeding practice to produce crossbreeds. Like I said in my other post, I think it would be really neat to produce a new breed of dog that could excel at sports and conformation as well as have stable temperaments. No matter how well a breeder knows the parents of a litter, it is still a mix of two breeds, and what comes out is not guaranteed to have a stable temperament or even great sporting capabilities.
I am not someone that is against dog sports. In fact, I think they are a great energy outlet and allow for people to bond with their dogs. I just think that there are so many different options other than sport mixes when looking for a performance dog. There are lines of dogs (especially BC's) that are bred specifically to be performance dogs. These dogs are great at what they do, and they are purebreds. Also, if someone is not looking for a puppy and doesn't mind their dog being altered, there is also the rescue option. I have seen many dogs adopted from the rescue I volunteer to be flyball, disc, agility, dog diving, SAR, and even hunting dogs.