To be fair, there are a lot of large dogs that an owner would struggle to hold back if they decided to go mad, things like GSD, Rottweilers, etc which have been around for centuries without causing any major problems. (Rottweilers are insanely intelligent and make good working dogs, as well as pets) but for the most part - these dogs are owned by responsible people.
For me, with the XLs, it's a unique situation where you have a dog which has been bred specifically to be as frightening as possible, so it attracts the type of owner who just doesn't care. They don't want a companion to love and spend time with, they just want something they can weaponise on the streets.
I think if you took an XL, trained it properly for the first critical 6 months, did socialisation as a full-time job (which you have to do, with a large breed) it would probably be fine... It would look scary - but it probably would be fine..
It's just the type of breed that attracts the worst type of owner and in the final analysis - it has become a problem breed because of this.