I agree with the core point that you cannot legislate for stupid. And bringing an unknown, powerful animal, without knowing its history, into a house with a toddler is stupid. There are a lot of stupid people about.
Also agree that the thinking around putting dogs to sleep needs to change. You see it on here all the time - a poster whose circumstances has changed, or who whose dog has always been aggressive, or whose dog has suddenly started nipping or biting. And the dog mad bunch always pile on with the same statements about dogs being for life, and how the poster made a commitment, and how the dog was there before the child, and how she should throw ££££ and behaviourists and trainers and special food and whatever else, that putting it down is absolutely the worst crime ever.
And if the OP tries the ££££ therapy for her dog and it's STILL aggressive and unpredictable, then she sticks it in a shelter and risks it going to another house, to be equally aggressive and unpredictable? Or the rescue pick up on the temperament, and keep it in kennels for the rest of its life?
No. Just put it to sleep and save yourself all the money and hassle. Why are people made to feel guilty for destroying a dangerous or aggressive animal?
And don't get me started on people who think it's a good idea to import these sorts of mutts from Eastern Europe.