Here in Belgium I believe that it depends on the sport and this is how I look at them.
Here we have KNPV (police dog training) and this is really hard. Only intented for the working dog and this means these dogs are very independent/strong minded. They are trained to bite "everywhere" (being outside of the training/trial field) and a lot of "civilian work". When trained properly ... no problemo. When trained poorly these dogs become a big risk (MY opinion). Luckily not everyone is allowed in this sport.
There's also (French) ringsport. This is intended for security dog training/breeders. Since they are not allowed to actually bite in the working field a part of the program is done with muzzle (protecting an object for example). Mostly malinois in this sport branch.
Then there is IPO/shutzhund. More open to "everyone"/breeders who want to do a sport. This is the "softest" version in my opinion, but still ... Wouldn't want to be the apache (the one that gets bitten)
A lot of people just do this for fun to be active with their dog.
They do define in almost all the schools that it is intented for "guarding dogs" (shepherds, malinois, bouvier, dobermann, ...) when you want to start training/compete.
This leads me to the fact that a more correct answer to your question would be:
These dogs were created to protect their owner (like a hunting dog is created for the hunting sport). Decades of breeding make that these dogs like these kind of "jobs". Can they be happy in a family without doing this sport ?? YES!! But one should look out for a "show line" breeder, not a dog from a working line. But these dogs just love to guard, like a border collie loves to herd or a pointer loves to search for prey etc ...
I know a lot of IPO dogs (they train this where I used to teach) and they do NOT bite without command. Most of the time it is a game for the dog and without the sleeve they "don't know" what to do. I do feel that all these dogs are more self confident.
The more the focus is on biting the civilian as they call it here, without focus on the sleeve, the more risk of biting incidents.
I know 2 police dogs and they are VERY social dogs, I do NOT fear them at all or feel the danger of getting a bite. With one of them (and the owner of course) we frequently go out for a walk and never did we have a problem. The new generation police dogs isn't the bite eager dog you used to see in the field, allthough they are still nasty when needed.
I think it is like in every sport. A responsible owner will get a good result being a controlled dog. People you wouldn't even give a hamster out of risk that they would make it a raging ball of fur get an uncontrolled dog. These last ones usually don't get far in the sport, but they create a bad image for the sport.
I don't think that this should be a delicate subject, because when trained properly this is an AWSOME sport !!!