I don’t think the anyone was saying that it takes a conspiracy theory to see that immigration policy is an ongoing political debate with politicians on either side.
But if you think everybody you disagree with is acting with secret ulterior motives that they never divulge publicly (or only in slip ups), you get a a lot closer to one.
But is that how it is debunked? Do newspapers, when addressing this conspiracy theory, write "Yes, our immigration policies could be likened to a great replacement, and will soon result in your minority status, but it is not a 'conspiracy' because we are doing it openly"?
And, if someone dislikes the results of such immigration policy, why would they care of the exact motives behind it? Even if you convince them it's not a conspiracy, their stance won't change.
But if you think everybody you disagree with is acting with secret ulterior motives that they never divulge publicly (or only in slip ups), you get a a lot closer to one.