Personally I doubt think it's just as high. But in any case, I'm not arguing for microplastics in particular as an explanation, just against the suggestion that IBD is some timeless human invariant that couldn't be attributed to peculiarities of the modern environment. (I find the hygiene-hypothesis-like explanations a little more compelling, although I don't have strong beliefs.) If the commenter wants to argue against microplastics as a cause, he needs to make claims like the one you made.