I could never get away with that, my dog weighs 60 pounds.
IMO, it's disrespectful to take your dog without asking into places that post notices that they don't allow animals.
But there are some places that don't allow animals that really should. Whenever I travel alone, I take my dog with me as a crime deterrent, and of course for the companionship too. Yet our highway rest stops and state park restrooms all post NO PETS signs, so what do you do if you're traveling alone with an animal in hot weather? I can't leave her in the car b/c of heatstroke, I can't leave the engine running w/ the AC on b/c it's against the law to leave a running vehicle unattended, it's not safe to leave her tied outside (theft, poisoning, abuse), but I can't take her into the bathroom with me.
I've broken that rule many times - she just comes in with me quietly. And it's not like rest stop toilets are the same thing as a restaurant or no-pets hotel room.
It would be nice if well-behaved dogs were allowed in more places - I would love to take my dog with me on combined errands to save fuel, on the way to/from the park (the nearest park is about 10 miles away), but I can't leave her in the car when it's hot. But I've also seen a lot of people who don't pick up after their dogs, and will just let them urinate & defecate all over everything
. Perhaps places could specify only dogs with a Canine Good Citizen certificate are allowed? That might even help foster an interest in obedience, leading hopefully to an increase in responsible dog ownership.