I think generally people here speak that way, but when you think about poly people even just in online spaces, it varies more.
I'll give you an example of how even here, the thinking varies a lot.
Fundamentally, I think the agreement to live with another autonomous adult means you can't hold them to agreements about things like guests or chores. Basically anything that's about how they choose to live in their space.
Of course I make agreements with people I live with and stick to them. But that's because I've chosen to live with those people and want us to enjoy some mutual happiness and comfort while we do. Those agreements aren't as numerous as one might think. It's mostly compatibility. I live with people who are compatible with my lifestyle and move on when we no longer match as well.
So you have platonic (?) roommates who just naturally are coming in with a shared idea of how doing chores should go. Whether that's taking out the trash, to sharing or not sharing food, cooking, clearing up clutter, taking care of pets, dishes in the sink/on the counter, who does the common rooms' floors, cleans the bathrooms, etc., etc. So you don't need to "hold them to agreements" because the agreements are naturally never an issue?
So for me, the very question of attempting to dictate when your partner brings their friends or lovers home doesn't exist in my world. How could I ever tell an adult they can't bring their chosen guests into their home?
I think when you have platonic roommates it is different than when you are living with a beloved romantic sex partner. Your domestic partner (non-platonic) may have been used to walking around the house naked or nearly so (assuming it was just the two of you and there were no additional platonic roomies). They may not want to see PDAs, they may not want another person having sex in their bed. I think people can get more territorial when living with their lover.
My gf pixi and I don't often like to share space often with our metamours because, in the past, several of my partners got crushes on pixi and that made things awkward, because we don't like to share partners. So we have an arrangement that is in between parallel and KTP. I think, even if I was living with a platonic roomie, if my bf came over and got a crush on her, it would be awkward. What if he broke up with me and kept coming over to date my roomie? Yikes.
Now, young poly people might be fine with that, I guess. (Or not?) Rob is dating Heather, and he gets a crush on her roommate Kyle. He keeps dating Heather and Kyle. Now suddenly you have a V all living together. Maybe they even have threeway sex! Woohoo! Then, for some reason, Rob and Heather break up, but Rob and Kyle don't, and Heather is in the next room and hears them having sex. Awkward and painful!
The downside of living with other adults is that they can live as they wish and I have little power to stop them. It's why I choose my housemates so carefully.
It's great to choose roommates carefully, for sure.
So when we have a topic that's about partners coming over, I have to shift my thinking towards it being an agreement issue. My instinct is to query why anyone thinks they can forbid someone from bringing guests to their home. To me, the only real ethical solution is to move into your own space. But when people come in with a "visiting metamour" issue, they already have a working relationship where they make "agreements" that quash the autonomy of the other. And they don't want to let go of that. There are too many benefits.
I guess, whether you're living with an actual partner, or just roomies, you all have to decide on them having guests... Not just the sex/poly part, but the noise levels, the use of the kitchen, the use of your "special cup!", hogging the TV, or watching obnoxious shows, god knows what. All the things that make people incompatible will hinder how it goes with guests.
I mean, my parents used to love to entertain. Usually it was cocktail parties or dinner parties, but often they had overnight guests. All guests start to smell like fish after 2 or 3 days. I think they all shared that feeling. And neither of them wanted to have guests over every day, especially during the week. Also, they might host guests, but there was an understanding that the guests would return the favor, so no one felt like they were shelling out for food and drink all the time.