Many, many, many scientists have asked this question. Many have made careers out of arguing the case.

But, the overwhelming majority of scientists that start out asking those questions ultimately land on the mainstream theories around dark matter and dark energy being our best, most consistent, and broadest ranging answers.

If someone were to come to them with a better theory that could explain more completely the sum total of these observations they would almost certainly be open minded about it.

So... is there really dark matter and dark energy? Probably. We've got a whole lot of evidence that isn't explained better by any alternatives. But I doubt any of these scientists would say it's totally impossible.