Dog theft is a HUGE thing, not that you'd know if you don't own a dog, but its big business.
Recognisable pedigrees particularly the popular breeds are stolen to be sold, or bred from.
Certain crossbreeds will also be stolen - lurchers for example for illegal hunting and breeding - poodle mixes for breeding or sales.
Some steal dogs to abuse them, use them as bait dogs and all can be stolen in order to ransome back to the owner.
Its a difficult crime to police, as whilst dogs are property, unlike most property they can also run away by themselves, get lost, bolt in a panic etc. Stolen dogs can be the other end of the country in a matter of a day. Too much pressure on known theives and the dogs just end up dead in a ditch somewhere.
A friends lurcher was stolen - and recovered 3 days later, 600 miles away, having been sold at least twice in that time, and from the state of her, someone had tried to work her as well.
Another friends lurcher nicked from over her garden fence - stolen for breeding we think. He was found dead in a hedge two days later, shot in the head, almost certainly because he was neutered and ear-tattooed.
A lovely lurcher I was thinking about adopting was stolen from the rescue kennels two days before I could take him - planned operation that involved at least three people putting out security cameras, cutting gates with bolt cutters, scoping the rescue out in the days/weeks before hand... not an opportunistic theft!
One of my dogs was snatched from outside a shop, I'd left him with a friend who sold the Big Issue (elderly chap and not capable of running after anyone) so I could go in the shopping centre that didn't allow dogs.
As I was heading to the exit doors, a young lad was running my way with my very panicked dog. I am so lucky he came into the shopping centre at that exact moment and obviously had no clue who I was...
Without thinking, I just grabbed the lead off him and started to yell at him to fuck off and he legged it... or I'd never have seen my dog again.
When I got back to my friend the poor guy was in tears asking everyone if they'd seen the lad, could they look, describing my dog and SO relieved I'd got him. The theif had chatted to him for a bit and then without warning shoved him over, snatched the lead and run off!
Dogs are stolen, daily, and from the nicest of places. Cars are broken into to take dogs, houses are broken into to take dogs. Leaving a dog tied up and unattended is just unthinkable these days for any responsible owner.
But even if it weren't - the owner is liable for whatever the dog does. If someone claims my dog bit them or lunged at them or barked at them and made them stumble and fall, even tied up... I am liable, I risk court, fines, dog control orders or even a destruction order on the dog. A dog without its owner, in public, is automatically 'out of control' because the owner is not present and for a dog to be 'dangerously out of control....' they only need to give someone 'reasonable apprehension of injury', they do not actually HAVE to bite someone!
Kids are a huge risk to tied up dogs, and at risk from them - I have lost track of how many times I've seen kids approach a tied up dog and try to hug it, stroke it, kick it, throw things at it or untie it and let it go. I've seen adults do similar things, I've even seen adults TELL their kids to go up to a strange, unattended dog and fuss or hug it.
So yep, if there are only two options - leave my dog somewhere unsafe, unattended, or take my dog somewhere my dog is not really supposed to be, at the potential minor inconvenience to a small number of people, but no actual risk to anyones safety... I know which I'll pick. That doesn't mean I parade my dogs around places they're not allowed, I plan and avoid having to do so on the whole but sometimes life puts you in a position where you have two crappy options and you have to pick one of them.