You're absolutely right, you don't know, you've assumed and are reacting on your assumption. They could own dogs at home, or snakes, or anything, could have even been to the toilet while on shift, so might the chef - which if we're assuming people don't bother washing their hands - means that you'd be refusing to use anywhere that employs humans that have to use the toilet or has anything in their home that you fear will contaminate your food? You clearly have a low opinion of the staff who serve you in such places so why use them at all?
Your call if you don't want to go anywhere with dogs present of course, but the result of that is less places to choose from.
I personally, love dogs and have 2, very occasionally I'll take them into a café to get a coffee on a walk if places don't offer service from a window for example but allow dogs, and get a takeaway anyway.
I don't sit in because although my two will just lie under the table quietly, so many people's dogs do not and that has an effect on mine when they're harassed by other people's poorly trained dogs.
And I don't think taking dogs shopping, dragging them around busy towns and cities or similar is in the dogs best interests, and I see it a lot working in a tourist place.
I've been tripped, snapped at and had to take food back and binned it, and had to have it remade because a dog jumped up at me while carrying the plates, but if we don't allow dogs then we lose a lot of trade and that could mean my job. And the place won't be open for people who don't like dogs to visit anyway.
Consumers like to dictate how businesses are run and who/what they allow in, at the moment a majority are dictating that their dog goes everywhere with them, so business is bowing to the consumer demand. Either consumers, by volume of demand, make the rules or the businesses do - and no one likes to be told where they can and can't go or what they can and can't do by a service business. It's exactly the environment created by customers demanding what they want and everything should work their way.