In any relationship, there’s usually an element of possesion or “belonging to”. That’s why we say “MY husband, MY wife, MY mother, MY father, MY brother, MY sister, MY friend, etc, etc” So to possess something doesn’t necessarily have to be a bad thing. It’s just that the word “possess” has many negative connotations, so we tend to automatically associate it with evil or ill intent. But all it means is to “belong to”. We usually don’t bat an eye when someone says something like, “you two belong together”. It’s a matter of semantics, really.
And generally, ppl tend to take care of and protect the things that belong to them, if they actually value and treasure them.
So possessing or belonging to a person does not mean that you own that person like you’d own a pet, a car, or a piece of property…it also does not mean that you can or should violate that person’s free will.
Think about it. How do you even get to the point where you can call a person, “your girlfriend” or “my girlfriend”? Doesn’t the other person have to agree to it in the first place?
So in the case of intimate relationships, you usually belong to someone (or someone belongs to you) based on a mutual agreement. From what I can tell, problems arise and things become toxic when you violate that agreement. And the issue with that is that many ppl enter into relationships having no idea what they’re agreeing to because they never discuss these things in the first place, but I’m going on a tangent, so I digress.
Basically, i think people hear the idea of “possessesion” in reference to relationships and have a kneejerk reaction to it because they don’t actually stop to consider what it means. They automatically jump to this extreme, slave situation in their heads where someone is being forced into a relationship against their own will, or in a relationship where someone treats them like a dog or worse. So the real concern here is not the terminology or the idea of possession, but it’s the fear of you or someone else having their free-will violated or abused.
CATS even stated that what’s good for one person isn’t going to necessarily be for other people which is itself objective, but when you start to get into the whole “this is toxic and wrong and this isn’t” etc then it’s a whole can of worms and all left up for interpretation because I can guarantee we could all list off things we find to be toxic and someone here won’t agree that it is. 
