Should pets board on public transport with their owners?

My opinion is that if, for example, a pet owner is polite, his dog will be polite as well, then wouldn't be problem with that. But I think that the pet have has to be have his documentation correctly, with all vacunes vaccinations, etc. And maybe if the pet is dangerous, this there should be a form of protection like a muzzle, or cage.

But, if the dog is not polite... it's very disturbing... Imagine a travel trip in pullman with a dog barking during for five hours in front of you... Buff...