We do not have any pets right now. One of the decisions we made together was that with our schedules, it wasn't fair to an animal to be penned up most of the time. We both love animals and someday, when we have time to treat it properly, we may get one.
I would have no problem with someone bringing a pet, as long as they asked first and took care of it's needs. We also have hardwood downstairs with carpeting upstairs, and when one of my friends brings her dog, we ask her to make sure it stays downstairs. She has no problem with that when she visits and she's vigilant. She has admitted that she wouldn't ever stay overnight with us, because her dog sleeps with her and since all of our bedrooms are upstairs she didn't want to crate it overnight downstairs, but it doesn't keep her from visiting. And I don't blame her, I would do the same thing. If I liked to sleep with my dog and I knew where I was going I couldn't, I would make other arrangements or not stay overnight.
I actually think that is probably another reason my DIL got mad at me in the beginning. She brought her dog with them one day and she immediately plopped it down on the couch. I didn't say anything as it really didn't bother me, but then it started digging into the leather couch and she didn't do anything. I finally asked her nicely to please put the dog down on the floor and she got all irritated and was ready to go.