I do believe all dogs (no matter the size or breed) should be kept on a lead in all public spaces. Not only for the safety of the public, but for the safety of the dog too.
There are MANY places specifically for having off lead dogs, if you look for them. I don't mean parks with easy entry/exit points either, there are fields that are fully enclosed with large fences that the owners charge fees to use, purposely for dogs to have off lead time. You can book onto slots where other dogs will be there or you can book private slots - I know this because I have been to many different ones with my dog, in order to do recall training with her in an open space and to also get her used to other dogs.
We also have a large garden for our dog to play in, and our garden is split into 2 with a fence, so that when the little one is outside playing, his area & toys are clean and left alone by the dog - and her area is for her to play. If we had a small garden, we wouldn't have a large dog.
There have been times where myself and the little one have had large breed or small breed dogs jumping up at us, getting too excited and behaving like idiots. This is simply down to the way in which the owner has trained them. Dogs jumping up/barking none stop/running around like lunatics, whatever the size is annoying and can be scary; but it can be prevented by having responsible owners.
My point is - banning all large breed dogs really would not solve the issue, there are plenty of small breed dogs with behavioural problems caused by their living environment/owners.
If we only had small breeds, you'd still get the big divide between those that behave and those that don't.
Not all big breeds are bad - just how not all small breeds are yappy little nipping brats, which again, wouldn't happen if their owners trained them correctly.