They're rather intimidating dogs even when they're not ripping small children to pieces. A woman who lives near us has one, was exercising it off the lead and publically berated my wife for 'teaching kids to be scared of dogs' when she took the long way round with the kids to avoid it. I've been bitten by dogs twice, am nervous around them and reckon my right to walk the streets unintimidated trumps others' right to walk around with 70 kilos of barely contained muscle and teeth. I'd be happy to see a ban and am unconcerned about the niceties of proving breeds. Err on the side of caution, not only will it prevent deaths it will hopefully make the kind of intimidating bullies that owe these things a little less capable of intimidation.