Yes I think it's all about being sensible.
My OH found a quote of 896 people in the States being killed by sheep, many of them from infected bites
Anke I think you are right that many Shetland sheep are kept by shepherdesses, often older, and that because Shetlands look so cuddly they forget they are also male sheep. A tup lamb which has been petted so is a bit mixed up about which species he is, may well just be trying to include his owner in with his harem.
I don't think Shetlands are intrinsically any more dangerous than tups of some other breeds, but all tups, all animals, all humans too for that matter, are potentially dangerous.
I would though suggest that Soay tups
are more aggressive than most (having watched them here up against Shetlands and multi-horned Hebs). This is perhaps due to the fact that on their native islands there are equal numbers of males to females, approximately, so tups have to compete to be successful at breeding, just as stags do. Even outside the breeding season a Soay tup has to establish himself in the pecking order. This has been his natural behaviour over thousands of years, with little intervention by Man, unlike most other breeds where there are far fewer tups per group of ewes, so not a lot to fight for.