The idea of "polluting" spacetime makes no more sense than humans "polluting" the natural organization of air molecules by displacing them by existing, or polluting the natural distribution of entropy by making decisions.
It's just bringing politics into a place where it doesn't belong.
"the presence in or introduction into the environment of a substance or thing that has harmful or poisonous effects."
I have no idea why you have this idea that polluting is some politicized term.
Your argument also doesn't hold considering that in the case we're talking about right now, the vast majority of spacetime is not inhabited nor is it regulated by anybody. Yet we're still able to talk about pollution because pollution in no way is tied towards a politicization of the conversation.
One could even go so far as to say you've polluted the conversation by including this "but you're making it political" distraction.
We are able talk about harm being done to insect populations or coastlines or any other inanimate objects. Again, humans, and their politics, aren't necessary.
I don't find my quoting of the definition as being petulant. I was wanting to frame the conversation around a shared definition of the word rather than asserting requirements.
It's true that it isn't a problem -- until it is.