Any sized dog can be dangerous, but obviously, a large dog can do more damage in the wrong hands.
My old dog weighed around 11 stone (of pure muscle), and towered over me when stood on her hind legs, but she was the soppiest and friendliest dog and was extremely well trained (I had over a year of one-on-one training sessions from being a pup). She was very well socialised, and attended festivals, etc, with us.
She was a St. Bernard, and at the time of getting her, there'd been issues with aggression in this breed occurring at around 2 years old (upon reaching maturity), so it can happen in any breed.
Most issues were, I believe, due to poor breeding practices, combined with inexperienced owners.
She was bought from an extremely reputable breeder, and we travelled 600 miles to visit them several times whilst she was there, and then to collect her at 10 to 12 weeks of age.
At the time of getting her, I'd owned dogs for 15 years and had walked them/been around them for around 20yrs, so I was experienced in dogs, including larger breeds (had GSDs before). We also had a elderly Golden Retriever and a younger medium-sized crossbreed.
Her head was bigger than my lap, and whilst she looked intimidating to some, she was the sweetest, most gentle dog, and great with my dc (and all children), so size doesn't mean bad, and a Jack Russsell could seriously maim a child, so it's not all about size.
What is needed is greater control over breeding (inc. the parents passing temperament checks), a limit on the number of times a dam or sire can be used/the profit that can be made, and some kind of licence scheme for large breed ownership.
@Canecorsomummy your dog sounds lovely, and you sound like a responsible owner. Good luck with her.