All terriers can be unpredictable. It is in their breeding to kill, we can't then blame the poor animal for acting on instincts we've refined in it.
The problem is, while most terriers are small yappy things (and as Ian says these dogs are always biting people) that can mostly just be ignored or laughed at (and Britain is a nation of lovers of these small yappy b*stards; in my opinion if you want a dog get a real dog; if you want a small animal get a cat. I've got both and they're both great), dogs like Staffordshire Bull Terriers, Pit Bulls (is American Staffordshire the correct name? Staffordshire is a county in England and Staffies are a different breed altogether, and to be honest a lot calmer than most of this type of dog) and English Bull Terriers are larger with big mouths and they can do a lot of damage in addition to their lack of predictability.
I've seen Bull Terriers who have been very well treated family pets turn on people, mostly the elderly or young children, on more than one occasion. I don't think they should be banned per se but muzzling them would be a step in the right direction.
(Incidentally, American Pit Bull Terriers are illegal in the UK).
-- jase, self-confessed Terrier hater (grrrrrr).
I mean, who the hell would own one of these runts, eh?
Jack Russell. Particularly nasty little tyke these can be
F****** Yorkshire Terrier. AAARRRGGGHH!!!!