To the people noting that labs and other similar breeds have higher bite incidents - they're simply not comparable. I am a dog trainer, so spend a lot of time out and about with all different kinds of dogs, I run social walks etc and we also work with owners of aggressive dogs - so have a good cross section of experience. We absolutely do get aggressive labs, spaniels, cockapoos, shepherds, rotties etc.
The big difference is the impact of that aggression.
I had an incident recently when an aggressive lab made a beeline for a client's dog and managed to get hold of the little dog. The dog on the receiving end had some minor injuries to the face and it took me about 30 seconds to get the lab off and under control.
Cross check with similar incident - a bully type went for one of our dogs out on a walk. One of our group is a man who is over 6 foot tall, probably weighs about 15 stone, and is a very experienced dog handler. The effort it took to get the dog off was unbelievable - it actually ended up taking two people to get the dog off, one punching it so hard that they broke bones in their hand, while someone else choked it out. It was like it was made of iron.
That's the difference.
I have my own dogs, one of whom is big and powerful, but not a bull breed, and I genuinely don't think he's a risk to the public. I would hate a world where all dogs are on lead or muzzled, I love my dogs to be able to have off lead time and freedom. However, XLs are built different, and putting an XL in the hands of an inexperienced dog owner is like giving a 16 year old a Ferrari. It's asking for trouble.